lxf: check the nb_streams instead of relying on padding

Remove the now unneeded stream pointer while at it.

Reported-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
CC: libav-stable@libav.org

libavformat/lxfdec.c

@@ -160,7 +160,7 @@ static int get_packet_header(AVFormatContext *s)
         break;
     case 1:
         //audio
-        if (!(st = s->streams[1])) {
+        if (s->nb_streams < 2) {
             av_log(s, AV_LOG_INFO, "got audio packet, but no audio stream present\n");
             break;
         }
@@ -171,6 +171,8 @@ static int get_packet_header(AVFormatContext *s)
         channels     = bytestream_get_le32(&p);
         track_size   = bytestream_get_le32(&p);
 
+        st = s->streams[1];
+
         //set codec based on specified audio bitdepth
         //we only support tightly packed 16-, 20-, 24- and 32-bit PCM at the moment
         st->codec->bits_per_coded_sample = (audio_format >> 6) & 0x3F;
@@ -288,7 +290,6 @@ static int lxf_read_packet(AVFormatContext *s, AVPacket *pkt)
 {
     LXFDemuxContext *lxf = s->priv_data;
     AVIOContext   *pb  = s->pb;
-    AVStream *ast = NULL;
     uint32_t stream;
     int ret, ret2;
 
@@ -302,7 +303,7 @@ static int lxf_read_packet(AVFormatContext *s, AVPacket *pkt)
         return AVERROR(EAGAIN);
     }
 
-    if (stream == 1 && !(ast = s->streams[1])) {
+    if (stream == 1 && s->nb_streams < 2) {
         av_log(s, AV_LOG_ERROR, "got audio packet without having an audio stream\n");
         return AVERROR_INVALIDDATA;
     }
@@ -317,7 +318,7 @@ static int lxf_read_packet(AVFormatContext *s, AVPacket *pkt)
 
     pkt->stream_index = stream;
 
-    if (!ast) {
+    if (!stream) {
         //picture type (0 = closed I, 1 = open I, 2 = P, 3 = B)
         if (((lxf->video_format >> 22) & 0x3) < 2)
             pkt->flags |= AV_PKT_FLAG_KEY;