Avoid the keyguard being a wallpaper target

When a dialog is shown above the keyguard and the keyguard becomes
invisible, the wallpaper flickers due to the destruction process of the
keyguard, which is targeted by the wallpaper.

Bug: 354094575
Test: manual test
1. Turn on the keyguard
2. Start a dialog on the keyguard

Change-Id: I5e50827492e24484e5ae02999109380ab09a2ee5
Signed-off-by: Hyeongseop Shim <hyeongseop.shim@samsung.corp-partner.google.com>