Allow ElementTabSet::RemoveTab to work on tabsets with no panels.

[exjam]

All the other methods in ElementTabSet seem to operate on tabs and panels independently, so why not this one too!

I bumped into this issue whilst using a tabset with no panels where I am using tabset in the same way that someone may use radio buttons.

[mikke89]

Thanks for the PR, nice to see first-time contributors!

This looks good to me. I'm curious to know more about how you use the tabset like this, if you'd like to share.

[exjam]

After making this PR I actually ended up moving to a data-for with buttons because I learnt that data-for doesn't work on tabset, and the use of data-for is what led me to my other PR for dynamic array indexing. We are very slowly replacing the custom UI system in an MMORPG, and what I have been working on recently is the chatbox - so I had tabs (now buttons) which were used to change the filtering on the chat message view. Instead of properly using tabs with a panel per chat tab, I just used the tab buttons to control the filtering of message types in the single message container.

[mikke89]

Very cool, glad to have you on-board! I'm always interested to hear more about projects and how they develop. Feel free to share some screenshots for the gallery too when you feel ready for that.