ptexTextureLoader: Fix a few compiler warnings
ptexTextureLoader: Fix a few compiler warnings

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