Unable to navigate through input history when message ends with "@" usernames

[jupjohn]

Checklist

• [X] I'm reporting a problem with Chatterino
• [X] I've verified that I'm running the most recent nightly build or stable release
• [X] I've looked for my problem on the wiki
• [X] I've searched the issues and pull requests for similar looking reports

Describe your issue

When navigating through input history with the arrow keys, messages ending in @usernames without a trailing space hijack the navigation.

This doesn't occur when normally tab/return-completing usernames - instead the automatically added space has to be removed (usually by moving the cursor elsewhere in the message and pressing return)

Screenshots

https://github.com/Chatterino/chatterino2/assets/4962764/0fa237a0-4d40-4d5e-a94e-3184edc5497d

OS and Chatterino Version

Chatterino 2.5.0 (commit 58a930d28) built with Qt 6.7.0 Running on Arch Linux, kernel: 6.8.7-zen1-1-zen