don't print garbage entries.

src/vm.c

@@ -169,6 +169,9 @@ cipush(mrb_state *mrb)
   mrb->ci->eidx = eidx;
   mrb->ci->ridx = ridx;
   mrb->ci->env = 0;
+  if (mrb->ci + 1 != mrb->ciend) {
+    mrb->ci[1].mid = 0;
+  }
   return mrb->ci;
 }