picture_pool: do not fail if pictures are available immediately

This avoids spurious errors in the decoders (and logs).

src/misc/picture_pool.c

@@ -244,14 +244,15 @@ picture_t *picture_pool_Wait(picture_pool_t *pool)
     vlc_mutex_lock(&pool->lock);
     assert(pool->refs > 0);
 
-    while (pool->available == 0 && !pool->canceled)
-        vlc_cond_wait(&pool->wait, &pool->lock);
-
+    while (pool->available == 0)
+    {
         if (pool->canceled)
         {
             vlc_mutex_unlock(&pool->lock);
             return NULL;
         }
+        vlc_cond_wait(&pool->wait, &pool->lock);
+    }
 
     i = ffsll(pool->available);
     assert(i > 0);