Clear credentials when the screen is locked

[varjolintu]

Fix for clearing the credentials when locking the screen.

Document visibility is hidden when the screen is locked. That kind of situation was not handled in the extension. The database hashes are updated only when the current document/page is visible. Now, when the document is hidden, all credentials are cleared just in case.

Fixes #357.

[droidmonkey]

This did not work for me. I went to a page that had credentials, they were loaded into the drop-down selection. I locked my computer and unlocked. When I returned KPXC was locked and the browser icon showed the locked icon, but the credentials were still loaded.

Why not call the clear credentials function when the icon is changed to the lock symbol?

P.S. - I am on Chrome / Win10

[varjolintu]

@droidmonkey Fixed. Check if it happens anymore.

[whisdol]

While testing this (merged into PR #387), I ran into the following scenario (FF65, Windows 10):

1. Open Firefox and a website with frames
2. Open KeePassXC
3. Click reconnect
4. Click into the username field, credentials are suggested in the autocomplete-dialog. They are not listed in the extension menu.
5. Close KeePassXC
6. Lock screen
7. Unlock screen
8. Click into login field.

In my tries, the credentials were not cleared and still suggested in the autocomplete-dialog.

On a website without frames, the credentials were cleared after step 5.

[varjolintu]

@whisdol Thanks! I'll check what causes this.

[whisdol]

This fix works for me, credentials are now (also) cleared after closing KeePassXC.