fix: Prevent domSelection.collapseToEnd crash in setDomSelection

[leondt1]

Description
At the beginning of the paragraph, composing text and then deleting all unconfirmed characters causes the value of domSelection.type to be None, leading to an error.

Issue
Fixes: (link to issue)

Example
A GIF or video showing the old and new behaviors after this pull request is merged. Or a code sample showing the usage of a new API. (If you don't include this, your pull request will not be reviewed as quickly, because it's much too hard to figure out exactly what is going wrong, and it makes maintenance much harder.)

Context
If your change is non-trivial, please include a description of how the new logic works, and why you decided to solve it the way you did. (This is incredibly helpful so that reviewers don't have to guess your intentions based on the code, and without it your pull request will likely not be reviewed as quickly.)

Checks

• The new code matches the existing patterns and styles.
• The tests pass with yarn test.
• The linter passes with yarn lint. (Fix errors with yarn fix.)
• The relevant examples still work. (Run examples with yarn start.)
• You've added a changeset if changing functionality. (Add one with yarn changeset add.)

[changeset-bot]

🦋 Changeset detected

Latest commit: e54a0f1

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
slate-react	Patch

Not sure what this means? Click here to learn what changesets are.

Click here if you're a maintainer who wants to add another changeset to this PR