fix correct stack postion for headless case

src/codegen.c

@@ -1205,7 +1205,9 @@ codegen(codegen_scope *s, node *tree, int val)
             pop();
             genop(s, MKOP_ABC(OP_SEND, cursp(), new_msym(s, mrb_intern(s->mrb, "===")), 1));
           }
-	  pop();
+          else
+	          pop();
+
           tmp = new_label(s);
           genop(s, MKOP_AsBx(OP_JMPIF, cursp(), pos2));
           pos2 = tmp;