Gromit-MPX replaces `~/.config/gromit-mpx.ini`

[Mathias Sven]

Describe the bug
Gromit-MPX replaces ~/.config/gromit-mpx.ini, this gets in the way of config managing software like Home-Manager from being able to operate properly.

Expected Behavior
If Gromit-MPX is to write to that file, and it is unable to due to it being read-only, it should fail the operation, not replace file.

Environment (please complete the following information):

• Gromit-MPX version: 1.4.3
• OS and version: NixOS

[Christian Beier]

Happy to merge a PR.