Long usernames can cause the cancel reply button to go outside of the window

Description

Long usernames can cause the cancel reply button to go outside the bounds of the window, making it unusable unless the window is resized.

Steps to reproduce

1. Open app
2. Go to #plasmamobile:kde.org
3. Start a reply to a message from @openwebdesigngermany_team:matrix.org

What is the current bug behavior?

Cancel reply button goes outside the bounds of the window, so it can't be used unless I resize the window

What is the expected correct behavior?

Cancel reply button should always be usable

Relevant logs and/or screenshots

Possible fixes

Probably needs to elide the "Replying to $username" string

System/Matrix Information

• Distribution / Platform: openSUSE Tumbleweed 20210330
• Qt Version: 5.15.2
• NeoChat version: git master commit 2cb81d12
• Quotient version: 0.6.6
• Matrix server: kde.org