BUG: Error pop up has no back button to exit error

[jesscmoore]

Describe the Bug

I get an error popup, when clicking on an external note with no data (because it is a note deleted by the owner without first revoking permission to me). However, there is no way to cancel the error popup to return to previous view. The only current option is to nav away using app bar or nav bar. All error popups should have an appropriately labelled button to escape the error screen. In this case, add a 'BACK' button to the alert dialog.

To Reproduce

Steps to reproduce the behaviour:

1. Open External Notes
2. Click on a note with the no data error in title line.
3. Error: no data found for note popup appears

Expected Behaviour

I can acknowledge the error by clicking OK or BACK.

Context

Where has the issue been observed:

• Android
• Chrome
• iOS
• Linux
• macOS
• Web
• Windows

[Add any other context about the problem here.]

App Version:
Flutter Version: 0.2.51

Closing Criteria

Checklist for closing the issue:

• make test
• make qtest
• I can click a button in the error dialog to return to previous screen.