Small clean up to how we validate the refiner when we build a PtexIndices.
Small clean up to how we validate the refiner when we build a PtexIndices.

shengfuintel/OpenSubdiv,poljere/OpenSubdiv,takahito-tejima/OpenSubdiv,c64kernal/OpenSubdiv,takahito-tejima/OpenSubdiv,xldeveloper/OpenSubdiv,shengfuintel/OpenSubdiv,anshuarya/OpenSubdiv,c64kernal/OpenSubdiv,xldeveloper/OpenSubdiv,xldeveloper/OpenSubdiv,shengfuintel/OpenSubdiv,nyotis/OpenSubdiv,c64kernal/OpenSubdiv,lookup1980/OpenSubdiv,nyotis/OpenSubdiv,lookup1980/OpenSubdiv,anshuarya/OpenSubdiv,takahito-tejima/OpenSubdiv,anshuarya/OpenSubdiv,nyotis/OpenSubdiv,poljere/OpenSubdiv,poljere/OpenSubdiv,lookup1980/OpenSubdiv