Additional NaN protection, check for correct refractive index, c-toe cleanup in Materials

Core/Algorithms/src/DecouplingApproximationStrategy.cpp

...Algorithms/src/LocalMonodisperseApproximationStrategy.cpp

Core/Core.pro

Core/PythonAPI/src/HomogeneousMaterial.pypp.cpp

Core/PythonAPI/src/IMaterial.pypp.cpp

Core/Samples/inc/HomogeneousMaterial.h

Core/Samples/inc/IMaterial.h

Core/Samples/inc/MaterialManager.h

Core/Samples/src/IMaterial.cpp

Core/Samples/src/MaterialManager.cpp

Core/Tools/inc/MathFunctions.h

Fit/Fit.pro

Tests/FunctionalTests/test_all.py