Don't return embedded HT from WeakMap get_gc() handler

This HT is embedded in the WeakMap and as such musn't be freed by
GC (or otherwise participate in GC). Instead add the values
contained in it to the GC buffer.

Author: nikic

Zend/zend_weakrefs.c

@@ -420,9 +420,13 @@ static HashTable *zend_weakmap_get_properties_for(zend_object *object, zend_prop
 static HashTable *zend_weakmap_get_gc(zend_object *object, zval **table, int *n)
 {
 	zend_weakmap *wm = zend_weakmap_from(object);
-	*table = NULL;
-	*n = 0;
-	return &wm->ht;
+	zend_get_gc_buffer *gc_buffer = zend_get_gc_buffer_create();
+	zval *val;
+	ZEND_HASH_FOREACH_VAL(&wm->ht, val) {
+		zend_get_gc_buffer_add_zval(gc_buffer, val);
+	} ZEND_HASH_FOREACH_END();
+	zend_get_gc_buffer_use(gc_buffer, table, n);
+	return NULL;
 }
 
 static zend_object *zend_weakmap_clone_obj(zend_object *old_object)