Null pointer dereference in OP_RETURN

[clayton-shopify]

The following input demonstrates a crash:

def a
  b { yield }
end

def b
  Fiber.new { yield }.resume
ensure
  a { break }
end

a

ASAN report:

ASAN:DEADLYSIGNAL
=================================================================
==98907==ERROR: AddressSanitizer: SEGV on unknown address 0x000000000018 (pc 0x00010ee28fc7 bp 0x7fff50f4a3d0 sp 0x7fff50f421a0 T0)
==98907==The signal is caused by a READ memory access.
==98907==Hint: address points to the zero page.
    #0 0x10ee28fc6 in mrb_vm_exec vm.c:2055
    #1 0x10ee0ea14 in mrb_vm_run vm.c:879
    #2 0x10ee068ae in mrb_run vm.c:2869
    #3 0x10ee416a0 in ecall vm.c:328
    #4 0x10ee252ab in mrb_vm_exec vm.c:1899
    #5 0x10ee0ea14 in mrb_vm_run vm.c:879
    #6 0x10ee444ef in mrb_top_run vm.c:2884
    #7 0x10ef1d2f8 in mrb_load_exec parse.y:5824
    #8 0x10ef1e125 in mrb_load_file_cxt parse.y:5833
    #9 0x10ecad693 in main mruby.c:227
    #10 0x7fffe5638234 in start (libdyld.dylib:x86_64+0x5234)

==98907==Register values:
rax = 0x0000000000000018  rbx = 0xf2f20000f2f2f200  rcx = 0x0000000000000018  rdx = 0x0000100000000003
rdi = 0x000061400000a460  rsi = 0x0000100000000000  rbp = 0x00007fff50f4a3d0  rsp = 0x00007fff50f421a0
 r8 = 0x0000100000000000   r9 = 0xc1d49033fac10000  r10 = 0x00007fff50f41b20  r11 = 0x00001e6f50f3b210
r12 = 0xf2f20000f1f1f1f1  r13 = 0x00001fffea1e92b8  r14 = 0xf2f20000f2f2f2f2  r15 = 0xf2f2f2f2f2040000
AddressSanitizer can not provide additional info.
SUMMARY: AddressSanitizer: SEGV vm.c:2055 in mrb_vm_exec
==98907==ABORTING
Abort trap: 6

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