[Enhancement] Allow saving empty tags with pet new -t

[craSH]

I like to use pet new -t as my default invocation (via a shell key bind), but sometimes I may not want to specify tags at the moment. It'd be nice if just hitting enter/saving an empty string in the Tags prompt would proceed as though -t were not specified, instead of needing to abort entirely at that point if you can't think of any tags to enter.

Thanks for the tool, I'm early on in my usage but I think it's going to be a lasting one!