check if $XAUTHORITY is set

[h-leth]

Solves #219

TO DO:

• Need to make a new Error type
• Should probably change these lines too, no need to set the environment variable again if its already set?

lemurs/src/post_login/x.rs

Lines 121 to 122 in 1d4be7d

	let xauth_path = xauth_path.to_str().ok_or(XSetupError::InvalidUTF8Path)?;
	process_env.set("XAUTHORITY", xauth_path);