matroska: set "done" only during resync fail.

Fixes playback of test7.mkv validation test file.
Signed-off-by: Reimar Döffinger <Reimar.Doeffinger@gmx.de>

libavformat/matroskadec.c

@@ -2420,7 +2420,6 @@ static int matroska_parse_cluster_incremental(MatroskaDemuxContext *matroska)
         }
     }
 
-    if (res < 0)  matroska->done = 1;
     return res;
 }