TypeError: unsupported operand type(s) for /: 'NoneType' and 'str'

Hello. When i launch protontricks with flag --gui its show not all games(only 2 of them) and when i select one of them its crashes.
```
pivnoi@pivnoi:~$ flatpak run com.github.Matoking.protontricks -v --gui
protontricks (INFO): Running inside Flatpak sandbox, version 1.6.5.
protontricks (WARNING): Flatpak version is too old (<1.12.1) to support sub-sandboxes. Disabling bwrap. --no-bwrap will be ignored.
protontricks (INFO): Found Steam directory at /home/pivnoi/.var/app/com.valvesoftware.Steam/data/Steam. You can also define Steam directory manually using $STEAM_DIR
protontricks (INFO): Using default Steam Runtime at /home/pivnoi/.steam/root/ubuntu12_32/steam-runtime
protontricks (INFO): WINETRICKS environment variable is not available. Searching from $PATH.
protontricks (INFO): Found 1 Steam library folders
protontricks (INFO): Currently logged-in Steam user: equesvasil
protontricks (INFO): Couldn't find custom shortcuts. Maybe none have been created yet?
protontricks (INFO): Using 'yad' as GUI provider
protontricks (INFO): Found active compatibility tool: Proton 5.13
protontricks (INFO): Active compatibility tool is a Proton installation
protontricks (INFO): WINE environment variable is not available. Setting WINE environment variable to Proton bundled version
Traceback (most recent call last):
File "/app/bin/protontricks", line 8, in
sys.exit(cli())
File "/app/lib/python3.9/site-packages/protontricks/cli/main.py", line 28, in cli
main(args)
File "/app/lib/python3.9/site-packages/protontricks/cli/util.py", line 143, in wrapper
return cli_func(self, *args, **kwargs)
File "/app/lib/python3.9/site-packages/protontricks/cli/main.py", line 220, in main
run_command(
File "/app/lib/python3.9/site-packages/protontricks/util.py", line 352, in run_command
str(proton_app.proton_dist_path / "bin" / "wine")
TypeError: unsupported operand type(s) for /: 'NoneType' and 'str'
```

Reproduce the crash with the reported `flatpak run com.github.Matoking.protontricks -v --gui` command. Start at `protontricks/cli/main.py` and follow the call into `protontricks/util.py`, especially `run_command` near the traceback. Done means the GUI lists the expected games and selecting one no longer raises the reported TypeError.

Written by the indexing model from the issue text.