Fix End Of Doc Crash

[thecoolwinter]

Description

Fixes a crash that occurred when editing the last characters in a file. This was missed by tests because it only appeared when syntax highlighting was applied.

Added a test case that catches this case in the styled range store. Added a second test in the highlighter tests that catches this and hopefully helps prevent some future bugs related to the highlighter.

Also added the package tests to the example app so tests can be run from the example project.

Related Issues

• 🐞 App crashes when pressing the delete key after typing incorrect code #284

Checklist

• I read and understood the contributing guide as well as the code of conduct
• The issues this PR addresses are related to each other
• My changes generate no new warnings
• My code builds and runs on my machine
• My changes are all related to the related issue above
• I documented my code

Screenshots

N/A