message: Fix typo in struct.h
diff: Name(Name &&) = default; \
  Name &operator=(const Name &) = default; \
  Name &operator=(Name &&) = default; \
  - template <typename... Ts> \
  - Name(const Name<Ts...> &v) \
  + template <typename... Ts> Name(const Name<Ts...> &v) \
  : ENOKI_MAPC(ENOKI_STRUCT_CONSTR_COPY, __VA_ARGS__) { } \
  - template <typename... Ts> \
  - Name(Name<Ts...> &&v) \
  + template <typename... Ts> Name(Name<Ts...> &&v) \
  : ENOKI_MAPC(ENOKI_STRUCT_CONSTR_MOVE, __VA_ARGS__) { } \
  template <typename... Ts> Name &operator=(Name<Ts...> &&v) { \
  ENOKI_MAP(ENOKI_STRUCT_ASSIGN_MOVE, __VA_ARGS__) \
  } \
  template <typename... Ts> Name &operator=(const Name<Ts...> &v) { \
  ENOKI_MAP(ENOKI_STRUCT_ASSIGN_COPY, __VA_ARGS__) \
  - return *this;
  + return *this; \
  + }
  #define ENOKI_STRUCT_SUPPORT(Name, ...) \
  NAMESPACE_BEGIN(enoki) \
  