HEMTT Clean fails with error when no optionals folder exists

[DerZade]

HEMTT Version: Commit 7137954
Project: https://github.com/DerZade/grad_slinghelmet/tree/hemtt

Description:
hemtt clean fails and throws an error when no optionals exists. The job works fine after adding an optionals directory (even when empty).

Steps to reproduce:

• Open a project without an optionals directory
• Run hemtt clean

Additional information:

HEMTT Output:

thread 'main' panicked at 'called `Result::unwrap()` on an `Err` value: Os { code: 3, kind: NotFound, message: "Das System kann den angegebenen Pfad nicht finden." }', src\libcore\result.rs:997:5
note: Run with `RUST_BACKTRACE=1` environment variable to display a backtrace. 

[jonpas]

https://github.com/synixebrett/HEMTT/blob/71379549b8d2eecc16af211647ca06c14075eee0/src/main.rs#L296 doesn't check if it exists.