MKV: Handle file with no duration or 0 duration

Close #6137
Fixes issue in http://forum.videolan.org/viewtopic.php?f=14&t=98525Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>
(cherry picked from commit 3c5f2a8c)
Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>

modules/demux/mkv/matroska_segment_parse.cpp

@@ -840,6 +840,7 @@ void matroska_segment_c::ParseInfo( KaxInfo *info )
 
     double f_dur = double(i_duration) * double(i_timescale) / 1000000.0;
     i_duration = mtime_t(f_dur);
+    if( !i_duration ) i_duration = -1;
 }
 
 

modules/demux/mkv/mkv.cpp

@@ -331,9 +331,13 @@ static int Control( demux_t *p_demux, int i_query, va_list args )
             return VLC_SUCCESS;
 
         case DEMUX_SET_POSITION:
+            if( p_sys->f_duration > 0.0 )
+            {
                 f = (double)va_arg( args, double );
                 Seek( p_demux, -1, f, NULL );
                 return VLC_SUCCESS;
+            }
+            return VLC_EGENERIC;
 
         case DEMUX_GET_TIME:
             pi64 = (int64_t*)va_arg( args, int64_t * );