v4l2codecs: decoder: Unmark previously pending request

requests are executed in order, so while dequeuing sink buffers for previous
request, also mark these request as no longer pending. This will allow reusing
the request later.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/1696>

sys/v4l2codecs/gstv4l2decoder.c

@@ -914,6 +914,7 @@ gst_v4l2_request_set_done (GstV4l2Request * request)
     while ((pending_req = gst_queue_array_pop_head (dec->pending_requests))) {
       gst_v4l2_decoder_dequeue_sink (request->decoder);
       g_clear_pointer (&pending_req->bitstream, gst_memory_unref);
+      pending_req->pending = FALSE;
 
       if (pending_req == request)
         break;