pthread: Immediately release all frames in ff_thread_flush()

Before this, they were only added to the delayed release queue and not
freed until later. This could lead to unnecessary memory use or buffer
exhaustion.
Signed-off-by: Ronald S. Bultje <rsbultje@gmail.com>

libavcodec/pthread.c

@@ -880,9 +880,13 @@ void ff_thread_flush(AVCodecContext *avctx)
     fctx->next_decoding = fctx->next_finished = 0;
     fctx->delaying = 1;
     fctx->prev_thread = NULL;
+    for (int i = 0; i < avctx->thread_count; i++) {
+        PerThreadContext *p = &fctx->threads[i];
         // Make sure decode flush calls with size=0 won't return old frames
-    for (int i = 0; i < avctx->thread_count; i++)
-        fctx->threads[i].got_frame = 0;
+        p->got_frame = 0;
+
+        release_delayed_buffers(p);
+    }
 }
 
 static int *allocate_progress(PerThreadContext *p)