message: Don't call libicu if input string is empty.
diff: @@ -40,15 +40,17 @@ Encoder::~Encoder() {
  }
  void Encoder::Encode(std::string& str) {
  - if (!_encoding.empty()) {
  - Convert(str, _conv_runtime, _conv_storage);
  + if (_encoding.empty() || str.empty()) {
  + return;
  }
  + Convert(str, _conv_runtime, _conv_storage);
  }
  void Encoder::Decode(std::string& str) {
  - if (!_encoding.empty()) {
  - Convert(str, _conv_storage, _conv_runtime);
  + if (_encoding.empty() || str.empty()) {
  + return;
  }
  + Convert(str, _conv_storage, _conv_runtime);
  }
  void Encoder::Init() {
  