Check if irep is NULL before print_backtrace()
According to the valgrind log attached to proc->body.irep
may be NULL in some cases.
@@ -118,6 +118,7 @@ each_backtrace(mrb_state *mrb, mrb_int ciidx, mrb_code *pc0, each_backtrace_func
if (MRB_PROC_CFUNC_P(ci->proc)) continue;
irep = ci->proc->body.irep;
+ if (!irep) continue;
if (mrb->c->cibase[i].err) {
pc = mrb->c->cibase[i].err;
