libmapper: fix the return value of osc_prefix_cmp() when different lengths.
libmapper: fix the return value of osc_prefix_cmp() when different lengths.

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