Fix circular dependencies in Relationship Graph

In the case where we have a cycle in parent-child relationships (i.e.
A -> B -> C -> A), the Relationship Graph fails with an INTERNAL
APPLICATION ERROR - Argument 1 passed to relgraph_add_child() must be of
type array, string given in core/relationship_graph_api.php line 427.

The recursive call was passing the bug id instead of the bug list.

Fixes #11381

core/relationship_graph_api.php

@@ -424,7 +424,7 @@ function relgraph_add_child( array &$p_bug_list, $p_bug_id ) {
 			$p_bug_list[$p_bug_id]->is_descendant = true;
 
 			foreach( $p_bug_list[$p_bug_id]->children as $t_child ) {
-				relgraph_add_child( $p_bug_id, $t_child );
+				relgraph_add_child( $p_bug_list, $t_child );
 			}
 		}
 	} else {