Preserve offsets set by demuxer

* In function vout_new_buffer offsets that are set in
  p_dec->p_owner->video could get lost before.

* Fixes problem with matroska clipping feature (#4600)
Modified-by: Laurent Aimar <fenrir@videolan.org>
Signed-off-by: Laurent Aimar <fenrir@videolan.org>

src/input/decoder.c

@@ -2352,11 +2352,15 @@ static picture_t *vout_new_buffer( decoder_t *p_dec )
             {
                 fmt.i_visible_width  = p_dec->fmt_in.video.i_visible_width;
                 fmt.i_visible_height = p_dec->fmt_in.video.i_visible_height;
+                fmt.i_x_offset       = p_dec->fmt_in.video.i_x_offset;
+                fmt.i_y_offset       = p_dec->fmt_in.video.i_y_offset;
             }
             else
             {
                 fmt.i_visible_width  = fmt.i_width;
                 fmt.i_visible_height = fmt.i_height;
+                fmt.i_x_offset       = 0;
+                fmt.i_y_offset       = 0;
             }
         }