Improve the warning issued when nans are discovered -- include the shader affected, not just the source line (since code in headers may be used in many shaders).
Improve the warning issued when nans are discovered -- include the shader
affected, not just the source line (since code in headers may be used in
many shaders).

tectronics/openshadinglanguage,qdtk/openshadinglanguage,h3rb/openshadinglanguage,tectronics/openshadinglanguage,h3rb/openshadinglanguage,h3rb/openshadinglanguage,qdtk/openshadinglanguage,qdtk/openshadinglanguage,tectronics/openshadinglanguage,h3rb/openshadinglanguage,tectronics/openshadinglanguage,qdtk/openshadinglanguage