Empty skm directory causing skm init to fail

[lsjurczak]

Hello,

thank you for this SSH key manager. It's really problematic to manage more than one key without it.

I found an issue when I had empty .skm directory.
skm init says SSH key store initialized! and it won't copy the SSH keys to the .skm directory.

I have a working fix and I would like to create a PR if you don't mind.

[TimothyYe]

@lsjurczak

Thanks lsjurczak, PR is welcome!
Please create your PR then I can review & merge it.