message: Don't check twice if ptex is there
diff: #ifndef VSNRAY_COMMON_PTEX_H
  #define VSNRAY_COMMON_PTEX_H 1
  -#include <common/config.h>
  -
  #include <memory>
  #include <string>
  -#if VSNRAY_COMMON_HAVE_PTEX
  #include <Ptexture.h>
  -#endif
  #include <visionaray/math/simd/type_traits.h>
  