Panics if no XDG Download folder is not set

[alexandru0-dev]

Issue:

if there is no XDG user folder is set for "Download", the option is None and unwrapping causes the panic:

rustdrop/rustdrop_core/src/core/config.rs

Line 41 in 82f4b37

dest: dirs::download_dir().unwrap().join("nearby"),

Possible solution:

Use a default dir or exit gracefully also notifying the user about the problem.