MKV: Use the appropriate time value to avoid loops

Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>
(cherry picked from commit fbdbd7da)
Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>

modules/demux/mkv/virtual_segment.cpp

@@ -390,7 +390,7 @@ bool virtual_segment_c::UpdateCurrentToChapter( demux_t & demux )
                         return true;
                     }
                 }
-                sys.i_start_pts = p_cur_chapter->p_chapter->i_start_time;
+                sys.i_start_pts = p_cur_chapter->i_virtual_start_time;;
             }
 
             p_current_chapter = p_cur_chapter;