Server crashes when fire charge touches mob

[mathiascode]

Expected behavior

A fire charge should hit a mob without causing a server crash.

Actual behavior

When a fire charge hits a mob, the server crashes. The following errors appear in the console:

*** Error in `./Cuberite': double free or corruption (!prev): 0x00007f4b7d8666d0 ***
======= Backtrace: =========
/lib/x86_64-linux-gnu/libc.so.6(+0x77725)[0x7f4b85f74725]
/lib/x86_64-linux-gnu/libc.so.6(+0x7ff4a)[0x7f4b85f7cf4a]
/lib/x86_64-linux-gnu/libc.so.6(cfree+0x4c)[0x7f4b85f80abc]
./Cuberite(_ZN6cWorld15TickQueuedTasksEv+0x1b7)[0x5c96a7]
./Cuberite(_ZN6cWorld4TickENSt6chrono8durationIlSt5ratioILl1ELl1000EEEES4_+0x289)[0x5b57f9]
./Cuberite(_ZN6cWorld11cTickThread7ExecuteEv+0x6c)[0x5b54dc]
/usr/lib/x86_64-linux-gnu/libstdc++.so.6(+0xb8c70)[0x7f4b86594c70]
/lib/x86_64-linux-gnu/libpthread.so.0(+0x76fa)[0x7f4b868656fa]
/lib/x86_64-linux-gnu/libc.so.6(clone+0x6d)[0x7f4b86003b5d]
======= Memory map: ========
00400000-00b7a000 r-xp 00000000 08:05 1970679                            /home/mathias/Downloads/Server/Cuberite
00d79000-00d7d000 rw-p 00779000 08:05 1970679                            /home/mathias/Downloads/Server/Cuberite
00d7d000-00d8b000 rw-p 00000000 00:00 0 
02cd5000-07123000 rw-p 00000000 00:00 0                                  [heap]
7f4b34000000-7f4b34021000 rw-p 00000000 00:00 0 
7f4b34021000-7f4b38000000 ---p 00000000 00:00 0 
7f4b3c000000-7f4b3c051000 rw-p 00000000 00:00 0 
7f4b3c051000-7f4b40000000 ---p 00000000 00:00 0 
7f4b40000000-7f4b40109000 rw-p 00000000 00:00 0 
7f4b40109000-7f4b44000000 ---p 00000000 00:00 0 
7f4b44000000-7f4b44021000 rw-p 00000000 00:00 0 
7f4b44021000-7f4b48000000 ---p 00000000 00:00 0 
7f4b4b7ff000-7f4b4b800000 ---p 00000000 00:00 0 
7f4b4b800000-7f4b4c000000 rw-p 00000000 00:00 0 
7f4b4c000000-7f4b4c025000 rw-p 00000000 00:00 0 
7f4b4c025000-7f4b50000000 ---p 00000000 00:00 0 
7f4b50000000-7f4b50021000 rw-p 00000000 00:00 0 
7f4b50021000-7f4b54000000 ---p 00000000 00:00 0 
7f4b54000000-7f4b54d59000 rw-p 00000000 00:00 0 
7f4b54d59000-7f4b58000000 ---p 00000000 00:00 0 
7f4b58000000-7f4b58504000 rw-p 00000000 00:00 0 
7f4b58504000-7f4b5c000000 ---p 00000000 00:00 0 
7f4b5c000000-7f4b5f72e000 rw-p 00000000 00:00 0 
7f4b5f72e000-7f4b60000000 ---p 00000000 00:00 0 
7f4b607f5000-7f4b607f6000 ---p 00000000 00:00 0 
7f4b607f6000-7f4b60ff6000 rw-p 00000000 00:00 0 
7f4b60ff6000-7f4b60ff7000 ---p 00000000 00:00 0 
7f4b60ff7000-7f4b617f7000 rw-p 00000000 00:00 0 
7f4b617f7000-7f4b617f8000 ---p 00000000 00:00 0 
7f4b617f8000-7f4b61ff8000 rw-p 00000000 00:00 0 
7f4b61ff8000-7f4b61ff9000 ---p 00000000 00:00 0 
7f4b61ff9000-7f4b627f9000 rw-p 00000000 00:00 0 
7f4b627f9000-7f4b627fa000 ---p 00000000 00:00 0 
7f4b627fa000-7f4b637ff000 rw-p 00000000 00:00 0 
7f4b637ff000-7f4b63800000 ---p 00000000 00:00 0 
7f4b63800000-7f4b64000000 rw-p 00000000 00:00 0 
7f4b64000000-7f4b64c2f000 rw-p 00000000 00:00 0 
7f4b64c2f000-7f4b68000000 ---p 00000000 00:00 0 
7f4b68000000-7f4b68504000 rw-p 00000000 00:00 0 
7f4b68504000-7f4b6c000000 ---p 00000000 00:00 0 
7f4b6c000000-7f4b6c40f000 rw-p 00000000 00:00 0 
7f4b6c40f000-7f4b70000000 ---p 00000000 00:00 0 
7f4b707f5000-7f4b707f6000 ---p 00000000 00:00 0 
7f4b707f6000-7f4b70ff6000 rw-p 00000000 00:00 0 
7f4b70ff6000-7f4b70ff7000 ---p 00000000 00:00 0 
7f4b70ff7000-7f4b717f7000 rw-p 00000000 00:00 0 
7f4b717f7000-7f4b717f8000 ---p 00000000 00:00 0 
7f4b717f8000-7f4b71ff8000 rw-p 00000000 00:00 0 
7f4b71ff8000-7f4b71ff9000 ---p 00000000 00:00 0 
7f4b71ff9000-7f4b72ffe000 rw-p 00000000 00:00 0 
7f4b72ffe000-7f4b72fff000 ---p 00000000 00:00 0 
7f4b72fff000-7f4b737ff000 rw-p 00000000 00:00 0 
7f4b737ff000-7f4b73800000 ---p 00000000 00:00 0 
7f4b73800000-7f4b74000000 rw-p 00000000 00:00 0 
7f4b74000000-7f4b74c5d000 rw-p 00000000 00:00 0 
7f4b74c5d000-7f4b78000000 ---p 00000000 00:00 0 
7f4b78000000-7f4b78504000 rw-p 00000000 00:00 0 
7f4b78504000-7f4b7c000000 ---p 00000000 00:00 0 
7f4b7c000000-7f4b7da70000 rw-p 00000000 00:00 0 
7f4b7da70000-7f4b80000000 ---p 00000000 00:00 0 
7f4b8007f000-7f4b80080000 ---p 00000000 00:00 0 
7f4b80080000-7f4b80880000 rw-p 00000000 00:00 0 
7f4b80880000-7f4b80881000 ---p 00000000 00:00 0 
7f4b80881000-7f4b81081000 rw-p 00000000 00:00 0 
7f4b81081000-7f4b81082000 ---p 00000000 00:00 0 
7f4b81082000-7f4b82087000 rw-p 00000000 00:00 0 
7f4b82087000-7f4b82088000 ---p 00000000 00:00 0 
7f4b82088000-7f4b82888000 rw-p 00000000 00:00 0 
7f4b82888000-7f4b82889000 ---p 00000000 00:00 0 
7f4b82889000-7f4b83089000 rw-p 00000000 00:00 0 
7f4b83089000-7f4b8308a000 ---p 00000000 00:00 0 
7f4b8308a000-7f4b84efb000 rw-p 00000000 00:00 0 
7f4b84efb000-7f4b84efc000 ---p 00000000 00:00 0 
7f4b84efc000-7f4b856fc000 rw-p 00000000 00:00 0 
7f4b856fc000-7f4b856fd000 ---p 00000000 00:00 0 
7f4b856fd000-7f4b85efd000 rw-p 00000000 00:00 0 
7f4b85efd000-7f4b860bd000 r-xp 00000000 08:05 2232911                    /lib/x86_64-linux-gnu/libc-2.23.so
7f4b860bd000-7f4b862bc000 ---p 001c0000 08:05 2232911                    /lib/x86_64-linux-gnu/libc-2.23.so
7f4b862bc000-7f4b862c0000 r--p 001bf000 08:05 2232911                    /lib/x86_64-linux-gnu/libc-2.23.so
7f4b862c0000-7f4b862c2000 rw-p 001c3000 08:05 2232911                    /lib/x86_64-linux-gnu/libc-2.23.so
7f4b862c2000-7f4b862c6000 rw-p 00000000 00:00 0 
7f4b862c6000-7f4b862dc000 r-xp 00000000 08:05 2232764                    /lib/x86_64-linux-gnu/libgcc_s.so.1
7f4b862dc000-7f4b864db000 ---p 00016000 08:05 2232764                    /lib/x86_64-linux-gnu/libgcc_s.so.1
7f4b864db000-7f4b864dc000 rw-p 00015000 08:05 2232764                    /lib/x86_64-linux-gnu/libgcc_s.so.1
7f4b864dc000-7f4b8664e000 r-xp 00000000 08:05 5647543                    /usr/lib/x86_64-linux-gnu/libstdc++.so.6.0.21
7f4b8664e000-7f4b8684e000 ---p 00172000 08:05 5647543                    /usr/lib/x86_64-linux-gnu/libstdc++.so.6.0.21
7f4b8684e000-7f4b86858000 r--p 00172000 08:05 5647543                    /usr/lib/x86_64-linux-gnu/libstdc++.so.6.0.21
7f4b86858000-7f4b8685a000 rw-p 0017c000 08:05 5647543                    /usr/lib/x86_64-linux-gnu/libstdc++.so.6.0.21
7f4b8685a000-7f4b8685e000 rw-p 00000000 00:00 0 
7f4b8685e000-7f4b86876000 r-xp 00000000 08:05 2232910                    /lib/x86_64-linux-gnu/libpthread-2.23.so
7f4b86876000-7f4b86a75000 ---p 00018000 08:05 2232910                    /lib/x86_64-linux-gnu/libpthread-2.23.so
7f4b86a75000-7f4b86a76000 r--p 00017000 08:05 2232910                    /lib/x86_64-linux-gnu/libpthread-2.23.so
7f4b86a76000-7f4b86a77000 rw-p 00018000 08:05 2232910                    /lib/x86_64-linux-gnu/libpthread-2.23.so
7f4b86a77000-7f4b86a7b000 rw-p 00000000 00:00 0 
7f4b86a7b000-7f4b86a82000 r-xp 00000000 08:05 2232845                    /lib/x86_64-linux-gnu/librt-2.23.so
7f4b86a82000-7f4b86c81000 ---p 00007000 08:05 2232845                    /lib/x86_64-linux-gnu/librt-2.23.so
7f4b86c81000-7f4b86c82000 r--p 00006000 08:05 2232845                    /lib/x86_64-linux-gnu/librt-2.23.so
7f4b86c82000-7f4b86c83000 rw-p 00007000 08:05 2232845                    /lib/x86_64-linux-gnu/librt-2.23.so
7f4b86c83000-7f4b86c86000 r-xp 00000000 08:05 2232912                    /lib/x86_64-linux-gnu/libdl-2.23.so
7f4b86c86000-7f4b86e85000 ---p 00003000 08:05 2232912                    /lib/x86_64-linux-gnu/libdl-2.23.so
7f4b86e85000-7f4b86e86000 r--p 00002000 08:05 2232912                    /lib/x86_64-linux-gnu/libdl-2.23.so
7f4b86e86000-7f4b86e87000 rw-p 00003000 08:05 2232912                    /lib/x86_64-linux-gnu/libdl-2.23.so
7f4b86e87000-7f4b86f8f000 r-xp 00000000 08:05 2232836                    /lib/x86_64-linux-gnu/libm-2.23.so
7f4b86f8f000-7f4b8718e000 ---p 00108000 08:05 2232836                    /lib/x86_64-linux-gnu/libm-2.23.so
7f4b8718e000-7f4b8718f000 r--p 00107000 08:05 2232836                    /lib/x86_64-linux-gnu/libm-2.23.so
7f4b8718f000-7f4b87190000 rw-p 00108000 08:05 2232836                    /lib/x86_64-linux-gnu/libm-2.23.so
7f4b87190000-7f4b871b6000 r-xp 00000000 08:05 2232906                    /lib/x86_64-linux-gnu/ld-2.23.so
7f4b87397000-7f4b8739e000 rw-p 00000000 00:00 0 
7f4b873b2000-7f4b873b5000 rw-p 00000000 00:00 0 
7f4b873b5000-7f4b873b6000 r--p 00025000 08:05 2232906                    /lib/x86_64-linux-gnu/ld-2.23.so
7f4b873b6000-7f4b873b7000 rw-p 00026000 08:05 2232906                    /lib/x86_64-linux-gnu/ld-2.23.so
7f4b873b7000-7f4b873b8000 rw-p 00000000 00:00 0 
7ffcd326e000-7ffcd328f000 rw-p 00000000 00:00 0                          [stack]
7ffcd3387000-7ffcd3389000 r--p 00000000 00:00 0                          [vvar]
7ffcd3389000-7ffcd338b000 r-xp 00000000 00:00 0                          [vdso]
ffffffffff600000-ffffffffff601000 r-xp 00000000 00:00 0                  [vsyscall]
[14:37:58]   D:    | Cuberite has encountered an error and needs to close
[14:37:58] Details | SIGABRT: Server self-terminated due to an internal fault
[14:37:58] Cuberite Jenkins clang x64 Release (master) build id: #477
[14:37:58] from commit id: 5265c6aaf6628b2ffebf9931120e49a3537ae75d built at: Sat 30 Apr 12:12:31 CEST 2016
./Cuberite(_Z15PrintStackTracev+0x19)[0x5e93a9]
./Cuberite[0x5d3375]
/lib/x86_64-linux-gnu/libc.so.6(+0x354a0)[0x7f4b85f324a0]
/lib/x86_64-linux-gnu/libc.so.6(gsignal+0x38)[0x7f4b85f32418]
/lib/x86_64-linux-gnu/libc.so.6(abort+0x16a)[0x7f4b85f3401a]
/lib/x86_64-linux-gnu/libc.so.6(+0x7772a)[0x7f4b85f7472a]
/lib/x86_64-linux-gnu/libc.so.6(+0x7ff4a)[0x7f4b85f7cf4a]
/lib/x86_64-linux-gnu/libc.so.6(cfree+0x4c)[0x7f4b85f80abc]
./Cuberite(_ZN6cWorld15TickQueuedTasksEv+0x1b7)[0x5c96a7]
./Cuberite(_ZN6cWorld4TickENSt6chrono8durationIlSt5ratioILl1ELl1000EEEES4_+0x289)[0x5b57f9]
./Cuberite(_ZN6cWorld11cTickThread7ExecuteEv+0x6c)[0x5b54dc]
/usr/lib/x86_64-linux-gnu/libstdc++.so.6(+0xb8c70)[0x7f4b86594c70]
/lib/x86_64-linux-gnu/libpthread.so.0(+0x76fa)[0x7f4b868656fa]
/lib/x86_64-linux-gnu/libc.so.6(clone+0x6d)[0x7f4b86003b5d]
Aborted

Steps to reproduce the behavior

1. Install the Essentials plugin (https://github.com/cuberite/Essentials)
2. Execute "/fireball small" in chat while looking at a mob

[mathiascode]

This also happens with wither skulls.