message: Fix vector_data failure under debug
diff: @@ -51,12 +51,12 @@ inline char string_back(const std::string &value) {
  template <typename T> inline T *vector_data(std::vector<T> &vector) {
  // In some debug environments, operator[] does bounds checking, so &vector[0]
  // can't be used.
  - return &(*vector.begin());
  + return vector.empty() ? nullptr : &vector[0];
  }
  template <typename T> inline const T *vector_data(
  const std::vector<T> &vector) {
  - return &(*vector.begin());
  + return vector.empty() ? nullptr : &vector[0];
  }
  template <typename T, typename V>
  