Apply suggestion from @pshriwise

Co-authored-by: Patrick Shriwise <[email protected]>

src/plot.cpp

@@ -317,7 +317,7 @@ void Plot::set_output_path(pugi::xml_node plot_node)
   }
   const std::string dir_if_present =
     filename.substr(0, filename.find_last_of("/") + 1);
-  if (!dir_exists(dir_if_present) and dir_if_present.size() > 0) {
+  if (dir_if_present.size() > 0 && !dir_exists(dir_if_present)) {
     fatal_error(fmt::format("Directory '{}' does not exist!", dir_if_present));
   }
   // add appropriate file extension to name