JNI: Fix "unknown signal type" when value=null in input handler.
JNI: Fix "unknown signal type" when value=null in input handler.

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