When setting a file path, valid characters not recognised properly

[TheWitness]

Describe the bug
When you goto the Settings > Paths page, and you enter a path with an underscore, a dash or a period, the setting is saved, but a warning is generated.

To Reproduce
Steps to reproduce the behavior:

1. Console > Configuration > Settings > Paths
2. Modify a folder to include one of the special characters
3. Attempt to save
4. See error

Expected behavior
These characters should not generate errors.