matroskaenc: add missing new line in av_log() call

Signed-off-by: Aurelien Jacobs <aurel@gnuage.org>

libavformat/matroskaenc.c

@@ -632,7 +632,7 @@ static int mkv_write_tracks(AVFormatContext *s)
                 put_ebml_uint(pb, MATROSKA_ID_TRACKTYPE, MATROSKA_TRACK_TYPE_SUBTITLE);
                 break;
             default:
-                av_log(s, AV_LOG_ERROR, "Only audio, video, and subtitles are supported for Matroska.");
+                av_log(s, AV_LOG_ERROR, "Only audio, video, and subtitles are supported for Matroska.\n");
                 break;
         }
         ret = mkv_write_codecprivate(s, pb, codec, native_id, qt_id);