hdr_reader: Fix a few compiler warnings
hdr_reader: Fix a few compiler warnings

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