Fixes #11029. Ensure AVPacket's data and size fields are initialized.

Without this initialization, mpegts_push_section() may try to access
uninitialized data and size fields from the AVPacket structure.

mythtv/external/FFmpeg/libavformat/utils.c

@@ -709,7 +709,7 @@ int ff_read_packet(AVFormatContext *s, AVPacket *pkt)
             }
         }
 
-        av_init_packet(pkt);
+        av_new_packet(pkt, 0);
         ret= s->iformat->read_packet(s, pkt);
         if (ret < 0) {
             if (!pktl || ret == AVERROR(EAGAIN))