fftools/thread_queue: do not return elements for receive-finished streams

It does not cause any issues in current callers, but still should not
happen.

fftools/thread_queue.c

@@ -164,7 +164,12 @@ static int receive_locked(ThreadQueue *tq, int *stream_idx,
     FifoElem elem;
     unsigned int nb_finished = 0;
 
-    if (av_fifo_read(tq->fifo, &elem, 1) >= 0) {
+    while (av_fifo_read(tq->fifo, &elem, 1) >= 0) {
+        if (tq->finished[elem.stream_idx] & FINISHED_RECV) {
+            objpool_release(tq->obj_pool, &elem.obj);
+            continue;
+        }
+
         tq->obj_move(data, elem.obj);
         objpool_release(tq->obj_pool, &elem.obj);
         *stream_idx = elem.stream_idx;
@@ -197,7 +202,14 @@ int tq_receive(ThreadQueue *tq, int *stream_idx, void *data)
     pthread_mutex_lock(&tq->lock);
 
     while (1) {
+        size_t can_read = av_fifo_can_read(tq->fifo);
+
         ret = receive_locked(tq, stream_idx, data);
+
+        // signal other threads if the fifo state changed
+        if (can_read != av_fifo_can_read(tq->fifo))
+            pthread_cond_broadcast(&tq->cond);
+
         if (ret == AVERROR(EAGAIN)) {
             pthread_cond_wait(&tq->cond, &tq->lock);
             continue;
@@ -206,9 +218,6 @@ int tq_receive(ThreadQueue *tq, int *stream_idx, void *data)
         break;
     }
 
-    if (ret == 0)
-        pthread_cond_broadcast(&tq->cond);
-
     pthread_mutex_unlock(&tq->lock);
 
     return ret;