Fix ptex indices computations for loop.
Fix ptex indices computations for loop.

The only method not yet implemented for loop in PtexIndices is GetAdjacency(), fix code accordingly.

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