avfilter/vf_subtitles: Remove unnecessary initialization of AVPacket

av_read_frame() can handle uninitialized packets.

Reviewed-by: Paul B Mahol <onemda@gmail.com>
Reviewed-by: Nicolas George <george@nsup.org>
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>

libavfilter/vf_subtitles.c

@@ -449,9 +449,6 @@ static av_cold int init_subtitles(AVFilterContext *ctx)
         ass_process_codec_private(ass->track,
                                   dec_ctx->subtitle_header,
                                   dec_ctx->subtitle_header_size);
-    av_init_packet(&pkt);
-    pkt.data = NULL;
-    pkt.size = 0;
     while (av_read_frame(fmt, &pkt) >= 0) {
         int i, got_subtitle;
         AVSubtitle sub = {0};