avcodec/apv_decode: set AVFrame.pkt_dts

Copy the dts of the decoded packet to the frame. decode.c does this only
for decoders with the decode callback, so it got lost when 084b67f6e3
moved the decoder to the receive_frame API, and frames decoded from
packets that carry only a dts have had no timestamp since.

Fixes: 084b67f6e3
Signed-off-by: Kacper Michajłow <kasper93@gmail.com>

libavcodec/apv_decode.c

@@ -513,6 +513,7 @@ static int apv_receive_frame_internal(AVCodecContext *avctx, AVFrame *frame)
         switch (pbu->type) {
         case APV_PBU_PRIMARY_FRAME:
             err = apv_decode(avctx, frame, pbu->content);
+            frame->pkt_dts = apv->pkt->dts;
             i++;
             goto end;
         case APV_PBU_METADATA: