iseq.c: use rb_check_funcall

* iseq.c (rb_iseq_load_iseq): use rb_check_funcall instead of
  repeating method search.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@53048 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

iseq.c

@@ -479,11 +479,10 @@ rb_iseq_new_with_opt(NODE *node, VALUE name, VALUE path, VALUE absolute_path,
 const rb_iseq_t *
 rb_iseq_load_iseq(VALUE fname)
 {
-    if (rb_respond_to(rb_cISeq, rb_intern("load_iseq"))) {
-	VALUE iseqv = rb_funcall(rb_cISeq, rb_intern("load_iseq"), 1, fname);
-	if (CLASS_OF(iseqv) == rb_cISeq) {
-	    return  iseqw_check(iseqv);
-	}
+    VALUE iseqv = rb_check_funcall(rb_cISeq, rb_intern("load_iseq"), 1, &fname);
+
+    if (!SPECIAL_CONST_P(iseqv) && RBASIC_CLASS(iseqv) == rb_cISeq) {
+	return  iseqw_check(iseqv);
     }
 
     return NULL;