message: Fix masking in ENOKI_VCALL_GETTER
diff: @@ -194,7 +194,8 @@ NAMESPACE_END(enoki)
  return zero<Result>(); \
  else \
  return enoki::gather<Result>(Result::steal(attr_id), \
  - UInt32::borrow(array.index()), mask); \
  + UInt32::borrow(array.index()), \
  + mask && enoki::neq(array, nullptr)); \
  } else { \
  return detail::vcall<Class>( \
  #name, [](auto self) \
  