mux: fix chunked interleaver

The code did not account properly for packets that where added to
the end of the packet list. Also flags for such packets where not
set correctly leading to incorrect chunked interleaving.

Reported-by: bcoudurier
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavformat/mux.c

@@ -549,20 +549,21 @@ int ff_interleave_add_packet(AVFormatContext *s, AVPacket *pkt,
         next_point = &s->packet_buffer;
     }
 
-    if (*next_point) {
     if (chunked) {
         uint64_t max= av_rescale_q_rnd(s->max_chunk_duration, AV_TIME_BASE_Q, st->time_base, AV_ROUND_UP);
         if (   st->interleaver_chunk_size     + pkt->size     <= s->max_chunk_size-1U
             && st->interleaver_chunk_duration + pkt->duration <= max-1U) {
             st->interleaver_chunk_size     += pkt->size;
             st->interleaver_chunk_duration += pkt->duration;
-                goto next_non_null;
         } else {
             st->interleaver_chunk_size     =
             st->interleaver_chunk_duration = 0;
             this_pktl->pkt.flags |= CHUNK_START;
         }
     }
+    if (*next_point) {
+        if (chunked && !(this_pktl->pkt.flags & CHUNK_START))
+            goto next_non_null;
 
         if (compare(s, &s->packet_buffer_end->pkt, pkt)) {
             while (   *next_point