MKV: init the index time to -1 as it was intended

As witnessed here git.videolan.org/?p=vlc.git;a=blob;f=modules/demux/mkv/matroska_segment.cpp;hb=HEAD#l1427
Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>

modules/demux/mkv/matroska_segment.cpp

@@ -129,7 +129,7 @@ void matroska_segment_c::LoadCues( KaxCues *cues )
             idx.i_track       = -1;
             idx.i_block_number= -1;
             idx.i_position    = -1;
-            idx.i_time        = 0;
+            idx.i_time        = -1;
             idx.b_key         = true;
 
             ep->Down();
@@ -953,7 +953,7 @@ void matroska_segment_c::Seek( mtime_t i_date, mtime_t i_time_offset, int64_t i_
     {
 
         for( ; i_idx < i_index; i_idx++ )
-            if( p_indexes[i_idx].i_time + i_time_offset > i_date )
+            if( p_indexes[i_idx].i_time != -1 && p_indexes[i_idx].i_time + i_time_offset > i_date )
                 break;
 
         if( i_idx > 0 )

modules/demux/mkv/mkv.cpp

@@ -468,7 +468,7 @@ static void Seek( demux_t *p_demux, mtime_t i_date, double f_percent, virtual_ch
             for( i_index = 0; i_index < p_segment->i_index; i_index++ )
             {
                 if( p_segment->p_indexes[i_index].i_position >= i_pos &&
-                    p_segment->p_indexes[i_index].i_time > 0 )
+                    p_segment->p_indexes[i_index].i_time != -1 )
                     break;
             }
             if( i_index == p_segment->i_index )