mrb_const_set may invoke const_added via mrb_funcall_argv, which
re-enters the VM and can reallocate cibase. This invalidates the
local ci pointer (and thus the regs macro that expands to ci->stack),
causing a use-after-free on the next opcode dispatch.
OP_SETMCNST and the OP_GET* / OP_*IDX opcodes already follow this
pattern; align OP_SETCONST with them.
Reported by OSS-Fuzz (clusterfuzz testcase 5886006653157376).
Co-authored-by: Claude <noreply@anthropic.com>
Yukihiro "Matz" Matsumoto
8a73faf61e