[lockscreen] Typed-in passcode is preserved on the lockscreen even after locking the device

Device:

• OS: postmarketOS edge aarch64 (updated today)
• Host: Pine64 PinePhone (1.2)
• Kernel: 5.13.12

Description:

When on the lockscreen, if a user types in a passcode without pressing the submit button, and locks their screen with the power button, the typed-in passcode will still be preserved after turning it back on again - allowing anyone to press "submit" to access the device.

Steps to Reproduce:

1. Turn on device
2. Use passcode to log in (it seems I cannot lock it without logging in first - another issue?)
3. Lock device and turn it back on
4. Type in full passcode without hitting the submit button
5. Lock device and turn it back on
6. Observe that the passcode is still available to be submitted

Expected Behavior:

Plasma Mobile would wipe anything that is typed in on the lockscreen upon locking the device, or at least bring back the default screen of the lockscreen.

Actual Behavior:

Plasma Mobile left me at the passcode screen open and did not wipe the typed-in passcode, potentially allowing access into the device.