Fix GH-13681: segfault when adding watchpoint fails.

thus when removing its entry, no watch point is set and crash on
pointer access.

Author: devnexen

sapi/phpdbg/phpdbg_watch.c

@@ -665,7 +665,7 @@ void phpdbg_watch_parent_ht(phpdbg_watch_element *element) {
 }
 
 void phpdbg_unwatch_parent_ht(phpdbg_watch_element *element) {
-	if (element->watch->type == WATCH_ON_BUCKET) {
+	if (element->watch && element->watch->type == WATCH_ON_BUCKET) {
 		phpdbg_btree_result *res = phpdbg_btree_find(&PHPDBG_G(watch_HashTables), (zend_ulong) element->parent_container);
 		ZEND_ASSERT(element->parent_container);
 		if (res) {
@@ -966,11 +966,14 @@ void phpdbg_remove_watchpoint(phpdbg_watchpoint_t *watch) {
 }
 
 void phpdbg_clean_watch_element(phpdbg_watch_element *element) {
-	HashTable *elements = &element->watch->elements;
 	phpdbg_unwatch_parent_ht(element);
-	zend_hash_del(elements, element->str);
-	if (zend_hash_num_elements(elements) == 0) {
-		phpdbg_remove_watchpoint(element->watch);
+
+	if (element->watch) {
+		HashTable *elements = &element->watch->elements;
+		zend_hash_del(elements, element->str);
+		if (zend_hash_num_elements(elements) == 0) {
+			phpdbg_remove_watchpoint(element->watch);
+		}
 	}
 }