[DRAFT] Fix regression: specifying IPC privileges using UID

[Cropi]

Recently, I came across an observation where it's not possible to specify the IPCAccessControlFiles using an UID instead of username/groupname. For example:

usbguard add-user 1000 --device list

Expected results: user with ID of 1000 can list devices Actual results: ERROR: IPC access control: invalid name format: 1002

That is because the isValidName() function does not allow having 'digit-only' names. I haven't experimented with the patch, will leave it here for discussion.

This was working in the past. Not sure if anyone is using it like this, so another possibility could be to leave it as it is and modify the documentation.