rsvg-handle: take viewport as pointer for get_geometry_for_element()
Vala has trouble with mixing out arguments and stack values. RsvgRectangle viewport can be passed as const pointer instead.
Apparently the API isn't fixed yet, let's propose a change while it is still time.
Related to: #454 (closed)
Signed-off-by: Marc-André Lureau marcandre.lureau@redhat.com