Period breaks mention

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Steps to reproduce

1. Write a talk message, start typing "@..." and select something from the mention popup. The mention pill is inserted followed by a space character.
2. Hit backspace to delete the space character (needed in some cases like you want to end a sentence with the mention or want a comma directly after the mention) and add a period (".") after the mention.
3. Send the message.

Expected behaviour

In the sent message, the mention should still work and be displayed as a pill.

Actual behaviour

In the sent message, the mention is broken and not displayed as a pill anymore.

Talk app

Talk app version: 23.0.6
Nextcloud version: 32/33

Start by reproducing the issue in the Talk app using the mention popup, then trace how a mention is represented when a message is sent after removing its trailing space and adding a period. Done means the sent message still displays the mention as a working pill in this punctuation case; the payload names no specific files or tests.