Fix emoji autocomplete when leading with a space

What does this MR do and why?

This MR fixes #322548 (closed) by removing a leading space from the emoji's matcher.

Screenshots or screen recordings

Before	After

How to set up and validate locally

1. Start local gdk
2. Visit an issue or MR
3. Enter Jean a dit : in the comment box and then follow the : with a space
4. The emoji picker should not be visible

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Thanks

Thanks so much to @jannik_lehmann @leetickett @jrushford && @cwoolley-gitlab for hopping on the pairing meeting to knock this out 🎉

Related to #322548 (closed)