LedDevicePhilipsHue: fix isNan sometimes not compile
LedDevicePhilipsHue: fix isNan sometimes not compile

sometime <cmath> is add automaticly, sometimes not. This leads to compile errors. Including <cmath> should fix this.

info taken from here:
http://en.cppreference.com/w/cpp/numeric/math/isnan
Funatiq/hyperion.ng,Funatiq/hyperion.ng,hyperion-project/hyperion.ng,redPanther/hyperion.ng,Funatiq/hyperion.ng,hyperion-project/hyperion.ng,hyperion-project/hyperion.ng,Funatiq/hyperion.ng,penfold42/hyperion.ng,penfold42/hyperion.ng,redPanther/hyperion.ng,hyperion-project/hyperion.ng,penfold42/hyperion.ng,redPanther/hyperion.ng,redPanther/hyperion.ng,penfold42/hyperion.ng,penfold42/hyperion.ng,redPanther/hyperion.ng,Funatiq/hyperion.ng,redPanther/hyperion.ng,hyperion-project/hyperion.ng,penfold42/hyperion.ng,Funatiq/hyperion.ng,hyperion-project/hyperion.ng