avformat/dashdec: Increase size of id buffer

The current size is not enough, see e.g.
http://ftp.itec.aau.at/datasets/DASHDataset2014/TearsOfSteel/1sec/TearsOfSteel_1s_simple_2014_05_09.mpd

Reviewed-by: Steven Liu <lq@chinaffmpeg.org>
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>

libavformat/dashdec.c

@@ -82,7 +82,7 @@ struct representation {
     AVFormatContext *ctx;
     int stream_index;
 
-    char id[20];
+    char id[32];
     char *lang;
     int bandwidth;
     AVRational framerate;