message: Add additional unbox overload for convenience
diff: @@ -787,6 +787,14 @@ T unbox(caf::optional<T> x) {
  return std::move(*x);
  }
  +/// Unboxes an optional value or fails the test if it doesn't exist.
  +template <class T>
  +T unbox(T* x) {
  + if (x == nullptr)
  + CAF_FAIL("x == nullptr");
  + return *x;
  +}
  +
  /// Expands to its argument.
  #define CAF_EXPAND(x) x
  