Can't change ROM_DIRECTORY if already configured one doesn't exist.
> oxyromon config -s ROM_DIRECTORY ~/games/emulation/
thread 'main' panicked at 'called `Result::unwrap()` on an `Err` value: SimpleError { err: "Failed to getcanonicalized path for /home/user/Emulation, could not canonicalize `/home/user/Emulation`" }', src/config.rs:149:73
Can't change ROM_DIRECTORY if already configured one doesn't exist.