Fix Png dependency in examples build (fixes screenshot ability in glViewer)
Fix Png dependency in examples build (fixes screenshot ability in glViewer)

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