compile.c: fix possible use of uninitialized value

LABEL::unremovable added by r58810 is not initialized by
new_label_body(), making the optimization unstable.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@58894 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

compile.c

@@ -1019,6 +1019,7 @@ new_label_body(rb_iseq_t *iseq, long line)
     labelobj->refcnt = 0;
     labelobj->set = 0;
     labelobj->rescued = LABEL_RESCUE_NONE;
+    labelobj->unremovable = 0;
     return labelobj;
 }