Crash when adding a new line right after a mention

[jmartinesp]

Problem

When adding a line break right after a mention, the composer crashes.

Steps to reproduce

• Add a mention to the composer. This will also add a whitespace after it.
• Remove the whitespace and place the cursor right after the mention.
• Hit enter/add a line break.

The composer crashes. This happens because when adding a new line we're supposed to split the DOM tree in 2 and use paragraphs/line break nodes in between, but the code doesn't make an exception for mentions, which have only 1 char length.

Related issues

Proposed solution

Fix the DOM tree splitting algorithm.