Caused by rB9cac5fa681c5 which fixed the handles for the camera border
gizmo (being much too small) -- which in turn was broken by rB98e4fbc7cc9e.

Camera border gizmo sets up its matrix_space a bit differently [this is
why we are getting very small values in gizmo_calc_rect_view_scale --
needs more investigation], but instead of breaking it for Light, Image
and Compositor Backdrop, lets just compensate by scaling the Camera
Border Gizmo for now.