hls: Don't check discard flags until the parent demuxer's streams actually exist

If passing the end of one segment while initializing the
chained demuxer, the parent demuxer's streams aren't set up
yet, so we can't recheck the discard flags.
Signed-off-by: Martin Storsjö <martin@martin.st>

libavformat/hls.c

@@ -427,7 +427,8 @@ reload:
     c->end_of_segment = 1;
     c->cur_seq_no = v->cur_seq_no;
 
-    if (v->ctx && v->ctx->nb_streams) {
+    if (v->ctx && v->ctx->nb_streams &&
+        v->parent->nb_streams >= v->stream_offset + v->ctx->nb_streams) {
         v->needed = 0;
         for (i = v->stream_offset; i < v->stream_offset + v->ctx->nb_streams;
              i++) {