Draft: app:images dockable: disable "Delete" on "New Display" action.

The first commit fixes #9285.

The second commit fixes an unreported issue.

See also #11642

Its a draft because it doesn't fix every GUI issue, and it is relatively unimportant (not really crashing, just CRITICALS), and it might be better for a larger fix. In the meantime, the draft shows how to quiet the CRITICALS, maybe only the first commit that quiets the CRITICALS should be merged.

Maybe a larger redesign is needed. The SET of open images might be an object, with signals. It would be the model, with two views: the Images dockable, and the Images tab bar. Currently, the two views don't seem to subscribe to enough events.