New Composer crashed Riot on attempting to create a user pill

[anoadragon453]

Description

I was just typing the beginning of someone's name in Riot and then hit tab, then the Riot tab closed.

Steps to reproduce

• Switch to new composer
• Start typing someone's name
• Hit tab
• Tab closed? Crashed? huh?

Describe how what happens differs from what you expected.

Logs being sent: yes

Version information

• Platform: web
• Browser: Firefox 70.0a1
• OS: Debian Buster
• URL: riot.im/develop

[anoadragon453]

So I was typing a name with an x in it. I typed the first few characters before the x, hit tab, the new composer didn't make a pill but just lost focus. Then I hit x which my VimiumFF plugin takes as "close tab". And the tab closed :)

So the real bug is to have tab pilling work.