message: timeout_handler: fix comment of test
diff: @@ -159,7 +159,8 @@ TEST(TimeoutHandler, NextTimeoutRemovedDuringCallback)
  th.add([&th, &cookie2]() {
  // This is evil but can potentially happen. We remove the other timer while
  - // being called. This triggers that the iterator is invalid and causes a segfault.
  + // being called. This triggers that the iterator is invalid and causes a segfault
  + // if not handled properly.
  th.remove(cookie2);
  }, 0.5, &cookie1);
  