Only insert null packets into the video que if there is a video stream.

Fixes memleak and should fix issue791.

Originally committed as revision 18629 to svn://svn.ffmpeg.org/ffmpeg/trunk

ffplay.c

@@ -2074,11 +2074,13 @@ static int decode_thread(void *arg)
             continue;
         }
         if(url_feof(ic->pb) || eof) {
+            if(is->video_stream >= 0){
             av_init_packet(pkt);
             pkt->data=NULL;
             pkt->size=0;
             pkt->stream_index= is->video_stream;
             packet_queue_put(&is->videoq, pkt);
+            }
             SDL_Delay(10);
             continue;
         }