Cannot open site profiles / unlock prompt does not appear

[kekukui]

Sometimes the unlock prompt does not appear after the database has been locked by the timer, so I cannot open site profiles. When the Keepass window is brought forward, the site list is shown instead of the unlock prompt. The toolbar and menus are operational, but all site profiles are shown in grey.

When I close this window using the 'X' button, the window is destroyed, but the app remains running in Task Manager. Launching the app from a taskbar shortcut creates a new instance of KeepassXC.exe. I must forcibly terminate all copies of KeepassXC.exe in Task Manager and re-launch in order to use the application.

## Steps to Reproduce

This issue occurs frequently, but it seems to be random -- I cannot reproduce it manually, and no errors are logged in Event Viewer.

## Debug Info

KeePassXC - Version 2.5.3
Revision: f8c962b

Qt 5.13.2
Debugging mode is disabled.

Operating system: Windows 10 (10.0)
CPU architecture: x86_64
Kernel: winnt 10.0.18363

Enabled extensions:

• Auto-Type
• Browser Integration
• SSH Agent
• KeeShare (signed and unsigned sharing)
• YubiKey

Cryptographic libraries: libgcrypt 1.8.5

[droidmonkey]

Your database is stuck in a save operation. Are you saving to a network share?

[droidmonkey]

This problem is being addressed through my PR: #4309