mkv: only use percentage of duration seeking when we have an seeking cues.

modules/demux/mkv.cpp

@@ -3467,7 +3467,7 @@ static void Seek( demux_t *p_demux, mtime_t i_date, double f_percent, chapter_it
     /* seek without index or without date */
     if( f_percent >= 0 && (config_GetInt( p_demux, "mkv-seek-percent" ) || !p_segment->b_cues || i_date < 0 ))
     {
-        if (p_sys->f_duration >= 0)
+        if( p_sys->f_duration >= 0 && p_segment->b_cues )
         {
             i_date = int64_t( f_percent * p_sys->f_duration * 1000.0 );
         }