MKV: workaround the seeking-to-0 issue on Win32

The faster way to seek does not work on win32, for some reason
Close #6006
(cherry picked from commit 3d4937278085b979683fe0db96e3516a75bc81c5)
Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>

modules/demux/mkv/matroska_segment.cpp

@@ -725,6 +725,7 @@ void matroska_segment_c::Seek( mtime_t i_date, mtime_t i_time_offset, int64_t i_
         }
     }
 
+#ifdef WIN32
     /* Don't try complex seek if we seek to 0 */
     if( i_date == 0 )
     {
@@ -738,6 +739,7 @@ void matroska_segment_c::Seek( mtime_t i_date, mtime_t i_time_offset, int64_t i_
         sys.i_pts = 0;
         return;       
     }
+#endif
 
     if ( i_index > 0 )
     {