when adding coauthors in the "go_xpost_save_post" hook, be sure to use the user nicename of the local user, and only call add_coauthors() if we have coauthors to add.

see https://github.com/GigaOM/legacy-pro/issues/2045
code sniffer happiness
Merge pull request #23 from wluo/github-2045

Finding Janko('s posts)!