An error for when there are no valid nicks.

[pinkisemils]

Hiya, whilst developing with your library, I noticed that invalid nicks result in a panic. I'm fairly certain that this isn't the expected behaviour. Here's my attempt at fixing this. If you think there's a better way to handle it, I'm open for suggestions or plain better fixes.

[aatxe]

Ah, great catch! Thanks! This should've been done when I eliminated the panic when no nicknames were specified at all, but was overlooked. Cheers!