txddemux: Limit allocated packets to filesize.

Fixes Ticket772
Bug found by: Diana Elena Muscalu
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavformat/txd.c

@@ -48,6 +48,9 @@ static int txd_read_header(AVFormatContext *s, AVFormatParameters *ap) {
     st->codec->time_base.den = 5;
     st->codec->time_base.num = 1;
     /* the parameters will be extracted from the compressed bitstream */
+
+    s->pb->maxsize= avio_size(s->pb);
+
     return 0;
 }