Previously, the clipping rectangle passed to
`meta_surface_actor_get_image()` was updated with the actual texture
size, but recent changes in `meta_shaped_texture_get_image()` now keep
the caller's clipping rectangle unchanged.
The implementation of `meta_window_actor_capture_into()` was relying on
the old behavior of updating the passed clipping rectangle, but now that
it's kept unchanged, the actual clipping rectangle used to copy the data
is wrong, which causes either a distorded image or worse, a crash of
mutter.
Use the resulting cairo image size to copy the data instead of the
clipping rectangle to avoid the issue and get the expected size.
Fixes: https://gitlab.gnome.org/GNOME/mutter/issues/442
3738579dd3