Astobj2: Ensure all calls to __adjust_lock pass a valid object.

__adjust_lock doesn't check for invalid objects, and doesn't have an
appropriate return value for invalid objects.  Most callers of
__adjust_lock pass objects that have already been confirmed valid,
this change adds checks before the remaining calls.

ASTERISK-24997 #close
Reported by: Corey Farrell

Change-Id: I669100f87937cc3f867cec56a27ae9c01292908f

main/astobj2_rbtree.c

@@ -878,6 +878,8 @@ static void rb_ao2_node_destructor(void *v_doomed)
 		 * same node.
 		 */
 		my_container = (struct ao2_container_rbtree *) doomed->common.my_container;
+		ast_assert(is_ao2_object(my_container));
+
 		__adjust_lock(my_container, AO2_LOCK_REQ_WRLOCK, 1);
 
 #if defined(AO2_DEBUG)