Fix phpGH-14652: segfault on node without document.

do not bother trying to clone the inner document if there is none to
begin with.

ext/dom/php_dom.c

@@ -584,7 +584,7 @@ static zend_object *dom_objects_store_clone_obj(zend_object *zobject) /* {{{ */
 
 	if (instanceof_function(intern->std.ce, dom_node_class_entry) || instanceof_function(intern->std.ce, dom_modern_node_class_entry)) {
 		xmlNodePtr node = (xmlNodePtr)dom_object_get_node(intern);
-		if (node != NULL) {
+		if (node != NULL && node->doc) {
 			php_dom_libxml_ns_mapper *ns_mapper = NULL;
 			if (php_dom_follow_spec_intern(intern)) {
 				if (node->type == XML_DOCUMENT_NODE || node->type == XML_HTML_DOCUMENT_NODE) {

ext/dom/tests/gh14652.phpt

@@ -0,0 +1,20 @@
+--TEST--
+GH-13960 (NULL bytes in XPath query)
+--EXTENSIONS--
+dom
+--CREDITS--
+YuanchengJiang
+--FILE--
+<?php
+function varToString($var) {
+}
+$attr = new DOMAttr('category', 'books');
+$script1_dataflow = $attr;
+class test {
+private function __clone() {
+}
+}
+$clone = clone $script1_dataflow;
+echo "OK"
+--EXPECT--
+OK