cosmetics: indentation and add a TODO comment

Originally committed as revision 11389 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/ac3dec.c

@@ -1114,6 +1114,7 @@ static int ac3_decode_frame(AVCodecContext * avctx, void *data, int *data_size,
             av_log(avctx, AV_LOG_ERROR, "frame CRC mismatch\n");
             return -1;
         }
+        /* TODO: error concealment */
     }
 
     avctx->sample_rate = s->sample_rate;