avformat/hlsenc: correctly reset subtitle stream counter per-varstream

Without resetting it, if there was a previous set of varstreams with
subtitles, it would subtract from all the streams, leading to chaos and
segfaults when trying to access for example stream -1.

libavformat/hlsenc.c

@@ -2416,7 +2416,6 @@ static int hls_write_packet(AVFormatContext *s, AVPacket *pkt)
     int is_ref_pkt = 1;
     int ret = 0, can_split = 1, i, j;
     int stream_index = 0;
-    int subtitle_streams = 0;
     int range_length = 0;
     const char *proto = NULL;
     int use_temp_file = 0;
@@ -2424,6 +2423,7 @@ static int hls_write_packet(AVFormatContext *s, AVPacket *pkt)
     char *old_filename = NULL;
 
     for (i = 0; i < hls->nb_varstreams; i++) {
+        int subtitle_streams = 0;
         vs = &hls->var_streams[i];
         for (j = 0; j < vs->nb_streams; j++) {
             if (vs->streams[j]->codecpar->codec_type == AVMEDIA_TYPE_SUBTITLE) {