fix overlap detection
fix overlap detection

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