Only use the XDG user data directory if it exists
Only use the XDG user data directory if it exists

Use the temp directory if the user data directory doesn't exist.

https://bugs.freedesktop.org/show_bug.cgi?id=57407

freedesktop-unofficial-mirror/realmd__realmd,freedesktop-unofficial-mirror/realmd__realmd,freedesktop-unofficial-mirror/realmd__realmd,freedesktop-unofficial-mirror/realmd__realmd