When switching from brat to PDF brat document data will be sent to PDF editor

[reckart]

Describe the bug
When using the automatic editor selection and switching from a document that renders in brat to a document that renders using the PDF editor, it can happen that a PushAnnotationsCommand ends up being sent to the PDF editor.

To Reproduce
Steps to reproduce the behavior:

1. Open the JS developer console
2. Open a document that auto-uses the brat editor
3. Switch to a document that uses the PDF editor

Expected behavior
The PDF editor should only receive data it can understand, so if there was a PushAnnotationsCommand still scheduled, it should probably be cancelled somehow.

Screenshots

Please complete the following information:

• Version and build ID: 32.0-beta-1