lavc/libvpxenc: handle queue desync more gracefully

If the packets returned by libvpx and our internal frame properties
queue get desynchronized for some reason (should not happen, but it is
not clear libvpx API guarantees this), we will keep adding to the queue
indefinitely and never remove anything.

Change the code to drain the queue even if timestamps do not match.

libavcodec/libvpxenc.c

@@ -401,11 +401,16 @@ static int frame_data_apply(AVCodecContext *avctx, AVFifo *fifo, AVPacket *pkt)
 {
     FrameData fd;
     uint8_t *data;
+    int ret = 0;
+
     if (av_fifo_peek(fifo, &fd, 1, 0) < 0)
         return 0;
-    if (fd.pts != pkt->pts)
-        return 0;
-    av_fifo_drain2(fifo, 1);
+    if (fd.pts != pkt->pts) {
+        av_log(avctx, AV_LOG_WARNING,
+               "Mismatching timestamps: libvpx %"PRId64" queued %"PRId64"; "
+               "this is a bug, please report it\n", pkt->pts, fd.pts);
+        goto skip;
+    }
 
 #if FF_API_REORDERED_OPAQUE
 FF_DISABLE_DEPRECATION_WARNINGS
@@ -419,20 +424,22 @@ FF_ENABLE_DEPRECATION_WARNINGS
         pkt->opaque_ref     = fd.frame_opaque_ref;
         fd.frame_opaque_ref = NULL;
     }
-    av_buffer_unref(&fd.frame_opaque_ref);
 
     if (fd.hdr10_plus) {
         data = av_packet_new_side_data(pkt, AV_PKT_DATA_DYNAMIC_HDR10_PLUS, fd.hdr10_plus->size);
         if (!data) {
-            av_buffer_unref(&fd.hdr10_plus);
-            return AVERROR(ENOMEM);
+            ret = AVERROR(ENOMEM);
+            goto skip;
         }
 
         memcpy(data, fd.hdr10_plus->data, fd.hdr10_plus->size);
-        av_buffer_unref(&fd.hdr10_plus);
     }
 
-    return 0;
+skip:
+    av_fifo_drain2(fifo, 1);
+    frame_data_uninit(&fd);
+
+    return ret;
 }
 
 static av_cold int codecctl_int(AVCodecContext *avctx,