There is a category setting that enforces 1 or more tags must be added to a topic from a specific tag group before creating it. This validation was not being run before the topic was being sent to a review queue for categories that have that setting enabled.
There was an existing validation in `TopicCreator` but it was not correct; it was only validating when the tags did _not_ exist and also only happened on `create`. I now run the validation in `TopicCreator.valid?`
I also improved the error message shown to the user when they have not added the tags required (showing the tag names from the tag group), and changed the composer tag selector to not show "optional" if there are N tags required from a certain group.
e3b1f5721b