Avoid reconciling when cloning into the same document (#14921)

We don't need to reconcile when we clone into the same document because
the namespace mapper is the same. Only when cloning into another
document is the namespace mapper different and do we need a
reconciliation.

Author: nielsdos

ext/dom/php_dom.c

@@ -2567,7 +2567,9 @@ xmlNodePtr dom_clone_node(php_dom_libxml_ns_mapper *ns_mapper, xmlNodePtr node,
 
 	if (ns_mapper != NULL) {
 		xmlNodePtr clone = dom_clone_helper(ns_mapper, node, doc, recursive);
-		if (EXPECTED(clone != NULL)) {
+		if (EXPECTED(clone != NULL) && doc != node->doc) {
+			/* We only need to reconcile the namespace when the document changes because the namespaces have to be
+			 * put into their respective namespace mapper. */
 			if (clone->type == XML_DOCUMENT_NODE || clone->type == XML_HTML_DOCUMENT_NODE || clone->type == XML_DOCUMENT_FRAG_NODE) {
 				for (xmlNodePtr child = clone->children; child != NULL; child = child->next) {
 					php_dom_libxml_reconcile_modern(ns_mapper, child);