Fixed rendering of subpictures with non 0 offset in direct3d.

It is needed for DVD menu support.

modules/video_output/msw/direct3d.c

@@ -1256,7 +1256,9 @@ static void Direct3DImportSubpicture(vout_display_t *vd,
         if (SUCCEEDED(hr)) {
             uint8_t  *dst_data   = lock.pBits;
             int       dst_pitch  = lock.Pitch;
-            uint8_t *src_data  = r->p_picture->p->p_pixels;
+            const int src_offset = r->fmt.i_y_offset * r->p_picture->p->i_pitch +
+                                   r->fmt.i_x_offset * r->p_picture->p->i_pixel_pitch;
+            uint8_t  *src_data   = &r->p_picture->p->p_pixels[src_offset];
             int       src_pitch  = r->p_picture->p->i_pitch;
             for (unsigned y = 0; y < r->fmt.i_visible_height; y++) {
                 int copy_pitch = __MIN(dst_pitch, r->p_picture->p->i_visible_pitch);