Null pointer dereference

[clayton-shopify]

The following input demonstrates a crash:

Hash.new{break}[0]

ASAN:DEADLYSIGNAL
=================================================================
==84356==ERROR: AddressSanitizer: SEGV on unknown address 0x000000000000 (pc 0x00010d24859d bp 0x7fff52b26190 sp 0x7fff52b1e960 T0)
    #0 0x10d24859c in mrb_vm_exec vm.c:1251
    #1 0x10d23da69 in mrb_vm_run vm.c:822
    #2 0x10d26f519 in mrb_top_run vm.c:2581
    #3 0x10d33e005 in mrb_load_exec parse.y:5760
    #4 0x10d33ee15 in mrb_load_file_cxt parse.y:5769
    #5 0x10d0da776 in main mruby.c:227
    #6 0x7fffb4357254 in start (libdyld.dylib+0x5254)

AddressSanitizer can not provide additional info.
SUMMARY: AddressSanitizer: SEGV vm.c:1251 in mrb_vm_exec
==84356==ABORTING
Abort trap: 6

This issue was reported by https://hackerone.com/icanthack

[matz]

The issue is caused by #3359