Fix signed/unsigned comparison warning.
Fix signed/unsigned comparison warning.

malloch/libmapper,libmapper/libmapper,malloch/libmapper,malloch/libmapper,libmapper/libmapper,libmapper/libmapper,radarsat1/libmapper,johnty/libmapper,libmapper/libmapper,libmapper/libmapper,malloch/libmapper,johnty/libmapper,malloch/libmapper,johnty/libmapper,malloch/libmapper,radarsat1/libmapper,johnty/libmapper,radarsat1/libmapper,radarsat1/libmapper,libmapper/libmapper,radarsat1/libmapper,johnty/libmapper