gallium/u_queue: assert that users must wait on fences before destroying them

Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Reviewed-by: Edward O'Callaghan <funfunctor@folklore1984.net>

src/gallium/auxiliary/util/u_queue.c

@@ -204,6 +204,7 @@ util_queue_fence_init(struct util_queue_fence *fence)
 void
 util_queue_fence_destroy(struct util_queue_fence *fence)
 {
+   assert(fence->signalled);
    pipe_condvar_destroy(fence->cond);
    pipe_mutex_destroy(fence->mutex);
 }