Starting a new paragraph in Safari sometimes doesn't insert text until after two keystrokes

Under some circumstances typing at the beginning of a new paragraph requires two keystrokes for text to start appearing.

##### Steps to Reproduce

1. Open https://trix-editor.org/ in Safari
2. Place caret at top of existing Trix document
3. Enter two short paragraphs (a single character each is enough)
4. Start a 3rd paragraph and type a single keystroke, it has no effect
5. Type a second keystroke, suddenly two characters are inserted at once

Clearing the entire document and starting over removes the bug, but adding a single paragraph and then starting over from step 1 (at the top of document) brings the bug back. In other words, there must be text below the caret for the bug to trigger.

##### Details

* Trix version: tried it on 2.0.7 through 2.0.10
* Browser name and version: Safari 17.3.1
* Operating system: macOS

Reproduce the issue at https://trix-editor.org/ in Safari 17.3.1 using the listed steps, then inspect the Trix editor behavior involved in starting a paragraph when text remains below the caret. Done means the first keystroke appears immediately and the two-keystroke reproduction no longer occurs.

Written by the indexing model from the issue text.