Bugfixes of reported issues and QoL improvements.
- removed special characters from paths derived from Preset names
- prevented using +screenshot_dir and -stdout for engines that don't support it
- save options.json to %appdata% if the current directory is not writable
- workaround for freezing file dialogs on some Linux desktop environments
- prevented showing "doesn't exist" warning when a path is empty (not set)
- fixed compatbility level "out of bounds" error when restoring with no engine selected
- fixed switching relative/absolute paths for selected map packs