Unable to rename Tag Group's title ("Save" button stays grayed-out)

[techAPJ (Arpit Jalan)]

@simon

I think that ideally the user would be told that a tag group needs to have at least one tag.

Done via:

https://github.com/discourse/discourse/commit/e54b5dadab9fa637d7e6a71c142fc97c0c9fda0c