fix: refocus canvas to pick up keystrokes

[arctan95]

Description

Fix mouseleave event triggered when clicking on the canvas

Resolved issues

Closes #5

[arctan95]

I've requested a small change, also let me know if you've tested it.

Does the same issue happen when you use noVNC (upstream) directly? Honestly, I've never been able to reproduce it 😓

Yes, this issue does exist upstream. The current approach is a little hacky indeed, hope the upstream will fix it soon.