When the list of current tags doesn't end with a comma, the new tag is jammed into the previous one

Issue Summary

Hi,
There are situations where the current tag list doesn't end with a comma.
Since tagtool doesn't add a comma before the new tag, choosing a tag from the tagtool dropdown jams the new tag into the previous tag.
This is especially apparent when editing an existing post and adding tags.

I believe that if autocomplete is launched, everything is fine (autocomplete replaces the last tag with the new selected tag).

Attached is a small patch for the JavaScript that checks if the current list ends with comma, and adds one if it doesn't.