Fix return NULL if admin was not created successfully in mdev_new().
Fix return NULL if admin was not created successfully in mdev_new().

johnty/libmapper,davidhernon/libmapper-admin2,davidhernon/libmapper-admin2,malloch/libmapper,radarsat1/libmapper,radarsat1/libmapper,davidhernon/libmapper,johnty/libmapper,malloch/libmapper,johnty/libmapper,libmapper/libmapper,radarsat1/libmapper,malloch/libmapper,johnty/libmapper,johnty/libmapper,libmapper/libmapper,libmapper/libmapper,libmapper/libmapper,libmapper/libmapper,davidhernon/libmapper,davidhernon/libmapper,radarsat1/libmapper,malloch/libmapper,libmapper/libmapper,malloch/libmapper,davidhernon/libmapper-admin2,radarsat1/libmapper,davidhernon/libmapper,davidhernon/libmapper,davidhernon/libmapper-admin2,davidhernon/libmapper-admin2,malloch/libmapper