message: explicitly save std::string when converting
diff: @@ -31,7 +31,8 @@ NSArray<NSString *> *Tokenize(Tokenizer *tokenizer, NSString *input) {
  NSArray<NSNumber *> *ConvertTokensToIds(Tokenizer *tokenizer, NSArray<NSString *> *tokens) {
  NSMutableArray<NSNumber *> *ret = [NSMutableArray arrayWithCapacity:[tokens count]];
  for (NSString *token in tokens) {
  - const char *cToken = MakeString(token).c_str();
  + std::string cc_token = MakeString(token);
  + const char *cToken = cc_token.c_str();
  int id;
  tokenizer->LookupId(cToken, &id);
  [ret addObject:[NSNumber numberWithInt:id]];
  