message: fix: don't attempt to create directories from empty paths
  We were taking parent paths of named outputs and tried to create output directories from it.
  When filename-only output flags were passed nextalign was crashing due to parent paths being empty.
  This adds checks for empty paths to prevent that.
diff: @@ -747,8 +747,15 @@ int main(int argc, char *argv[]) {
  const auto paths = getPaths(cliParams, genes);
  logger.info(formatPaths(paths));
  - fs::create_directories(paths.outputFasta.parent_path());
  - fs::create_directories(paths.outputInsertions.parent_path());
  + const auto outputFastaParent = paths.outputFasta.parent_path();
  + if (!outputFastaParent.empty()) {
  + fs::create_directories(outputFastaParent);
  + }
  +
  + const auto outputInsertionsParent = paths.outputInsertions.parent_path();
  + if (!outputInsertionsParent.empty()) {
  + fs::create_directories(outputInsertionsParent);
  + }
  std::ofstream outputFastaFile(paths.outputFasta);
  if (!outputFastaFile.good()) {
  