Deleting emojis sometimes only deletes part of them, leads to weird characters send

#### Describe the bug
While trying to find the cause of #3449 I instead found a different issue that I've occasionally seen before:

#### To Reproduce
Steps to reproduce the behavior:
1. Type `:;`
2. Select the :wink: emoji from the completer
3. Use backspace once, the emoji will still be there
4. Send message
5. See that a `?` message got sent

This was tested on Gboard and SimpleKeyboard (from F-Droid)

#### Expected behavior
Emoji gets properly deleted on backspace

#### Smartphone (please complete the following information):
- Device: Pixel 4a
- OS: Android 11

#### Additional context
- 1.1.8 from Gplay