message: fix: prevent crash when an optional path cli arg is not provided
diff: @@ -32,7 +32,7 @@ namespace Nextclade {
  * Opens a file stream, if the given optional filepath contains value, returns nullptr otherwise
  */
  inline std::unique_ptr<std::ostream> openOutputFileMaybe(const std::optional<std::string> &filepath) {
  - if (!filepath) {
  + if (!filepath || filepath->empty()) {
  return nullptr;
  }
  