Null pointer dereference in mrb_obj_iv_get

[clayton-shopify]

The following input demonstrates a crash:

b = []
c = (0..0)
d = 0
e = ""
begin
  z = x
rescue
end
1.instance_exec {
  begin
    break
    Proc.new{}
  ensure
    def l
    end
  end
}
z.inspect

ASAN report:

ASAN:DEADLYSIGNAL
=================================================================
==54237==ERROR: AddressSanitizer: SEGV on unknown address 0x000000000018 (pc 0x000104f2c817 bp 0x7fff5ae09890 sp 0x7fff5ae09720 T0)
==54237==The signal is caused by a READ memory access.
==54237==Hint: address points to the zero page.
    #0 0x104f2c816 in mrb_obj_iv_get (mruby:x86_64+0x100141816)
    #1 0x104e2b13c in mrb_class_path (mruby:x86_64+0x10004013c)
    #2 0x104e2c97f in mrb_class_name (mruby:x86_64+0x10004197f)
    #3 0x104e2d462 in mrb_obj_classname (mruby:x86_64+0x100042462)
    #4 0x104ec84ea in mrb_any_to_s (mruby:x86_64+0x1000dd4ea)
    #5 0x104e9111f in mrb_method_missing (mruby:x86_64+0x1000a611f)
    #6 0x104f5910b in mrb_vm_exec (mruby:x86_64+0x10016e10b)
    #7 0x104f4e654 in mrb_vm_run (mruby:x86_64+0x100163654)
    #8 0x104f840ff in mrb_top_run (mruby:x86_64+0x1001990ff)
    #9 0x10505c26d in mrb_load_exec (mruby:x86_64+0x10027126d)
    #10 0x10505d085 in mrb_load_file_cxt (mruby:x86_64+0x100272085)
    #11 0x104ded3a3 in main mruby.c:227
    #12 0x7fffe5638234 in start (libdyld.dylib:x86_64+0x5234)

==54237==Register values:
rax = 0x0000000000000018  rbx = 0x00007fff5ae09780  rcx = 0x000061400000a440  rdx = 0x00001fffeb5c12e4
rdi = 0x00007fff5ae09740  rsi = 0x0000000000000000  rbp = 0x00007fff5ae09890  rsp = 0x00007fff5ae09720
 r8 = 0x00007fff5ae09760   r9 = 0x00000000000002a7  r10 = 0x0000000000000018  r11 = 0x0000100000000003
r12 = 0x00007fff5ae098e0  r13 = 0x00007fff5ae09900  r14 = 0x0000100000000000  r15 = 0x00007fff5ae098c0
AddressSanitizer can not provide additional info.
SUMMARY: AddressSanitizer: SEGV (mruby:x86_64+0x100141816) in mrb_obj_iv_get
==54237==ABORTING
Abort trap: 6

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

[Asmod4n]

This is a dupe of #3708, full trace is available there.