fix /0 bug
fix /0 bug

real image / real image failed for rhs == 0

lovell/libvips,jcupitt/libvips,jcupitt/libvips,mcanthony/libvips,mcanthony/libvips,leiyangyou/libvips,wishabi/libvips,wishabi/libvips,wishabi/libvips,jcupitt/libvips,leiyangyou/libvips,leiyangyou/libvips,wishabi/libvips,lovell/libvips,lovell/libvips,jcupitt/libvips,mcanthony/libvips,leiyangyou/libvips,lovell/libvips,mcanthony/libvips