Improved NaN filtering for DNI
Improved NaN filtering for DNI

(cherry picked from commit e69ecf32e1c0787998c476e1f806ce32aa11b4d8)

Conflicts:
	pvlib/clearsky.py

jforbess/pvlib-python,dacoex/pvlib-python,alorenzo175/pvlib-python,MoonRaker/pvlib-python,ianctse/pvlib-python,wholmgren/pvlib-python,pvlib/pvlib-python,uvchik/pvlib-python,cwhanse/pvlib-python,mikofski/pvlib-python,anomam/pvlib-python,rubennj/pvlib-python