Throw Error exception in DOM_GET_OBJ

Per general convention for handling of uninitialized objects.

Author: nikic

ext/dom/php_dom.h

@@ -140,8 +140,8 @@ entry = zend_register_internal_class_ex(&ce, parent_ce);
 #define DOM_GET_OBJ(__ptr, __id, __prtype, __intern) { \
 	__intern = Z_DOMOBJ_P(__id); \
 	if (__intern->ptr == NULL || !(__ptr = (__prtype)((php_libxml_node_ptr *)__intern->ptr)->node)) { \
-  		php_error_docref(NULL, E_WARNING, "Couldn't fetch %s", ZSTR_VAL(__intern->std.ce->name));\
-  		RETURN_NULL();\
+		zend_throw_error(NULL, "Couldn't fetch %s", ZSTR_VAL(__intern->std.ce->name));\
+		RETURN_THROWS();\
   	} \
 }