electronicarts: prevent endless loop opportunity in process_audio_header_elements()

Fixes issue2529.

Originally committed as revision 26302 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavformat/electronicarts.c

@@ -113,6 +113,8 @@ static int process_audio_header_elements(AVFormatContext *s)
         int inSubheader;
         uint8_t byte;
         byte = get_byte(pb);
+        if (!byte)
+            break;
 
         switch (byte) {
         case 0xFD: