Edit content button fails in the Channel Manager when a document has a pending request

When a document has a pending workflow request on it, for example a publication request, its not possible to open that in edit mode. When using the Channel Manager, a document may have a "Edit content" button. When you click that for this document, nothing happens. The functionality is broken.

The problem is here that opening the document in edit mode is not permitted. A stack trace appears in the logs, with as main messages:

• ERROR [org.onehippo.cms7.channelmanager.templatecomposer.PageEditor$1.onEvent():216] Could not open editor for document
• Caused by: org.hippoecm.repository.api.WorkflowException: unable to edit document with pending operation

These are some options to fix this that I can think of:
1. the document should be opened in view mode (which I would prefer as the default behavior anyway instead of the edit mode)
2. the edit content button must be disabled for these kind of documents
3. the user is warned that opening is not possible because of the pending request