fix a cache warning
fix a cache warning

you can now call vips_cache_set_max() and friends just after
vips_init() ... previously you had to wait for the cache to be built

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