avcodec/pcm_rechunk_bsf: unref packet before putting a new one in

Fixes: memleak
Fixes: 45982/clusterfuzz-testcase-minimized-ffmpeg_BSF_PCM_RECHUNK_fuzzer-5562089618407424

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/pcm_rechunk_bsf.c

@@ -151,7 +151,8 @@ static int rechunk_filter(AVBSFContext *ctx, AVPacket *pkt)
                 av_packet_move_ref(pkt, s->in_pkt);
                 return send_packet(s, nb_samples, pkt);
             }
-        }
+        } else
+            av_packet_unref(s->in_pkt);
 
         ret = ff_bsf_get_packet_ref(ctx, s->in_pkt);
         if (ret == AVERROR_EOF && s->out_pkt->size) {