mkv muxer: fix the crash when agent == NULL

diff --git a/src/muxer/muxer_mkv.c b/src/muxer/muxer_mkv.c
index f9940ec3e6fb49bfdc087b7e4ac87237f374c3a3..755dbad1d86ebeafc03db4013b20e66f9fb0583e 100644 (file)
--- a/src/muxer/muxer_mkv.c
+++ b/src/muxer/muxer_mkv.c
@@ -1544,7 +1544,8 @@ mkv_muxer_create(const muxer_config_t *m_cfg,
   /*
    * VLC has no support for MKV S_DVBSUB codec format
    */
-  mk->dvbsub_skip    = strstr(agent, "LibVLC/") != NULL;
+  if (agent)
+    mk->dvbsub_skip  = strstr(agent, "LibVLC/") != NULL;
 
   TAILQ_INIT(&mk->holdq);