avcodec/pcm_rechunk_bsf: assert that in_pkt is empty after merging its data into out_pkt

If it's not empty here, then a leak would ocurr immediately after.

Signed-off-by: James Almer <jamrial@gmail.com>

libavcodec/pcm_rechunk_bsf.c

@@ -139,6 +139,7 @@ static int rechunk_filter(AVBSFContext *ctx, AVPacket *pkt)
                     av_packet_move_ref(pkt, s->out_pkt);
                     return send_packet(s, nb_samples, pkt);
                 }
+                av_assert0(!s->in_pkt->size);
             } else if (s->in_pkt->size > data_size) {
                 ret = av_packet_ref(pkt, s->in_pkt);
                 if (ret < 0)