Finish MediaProj..Perm..Activity if Keyguard is dismissed

Finish the MediaProjectionPermissionActivity if Keygaruad is dismissed

Bug: 351409536
Flag: com.android.systemui.media_projection_dialog_behind_lockscreen
Test: Manually: start Meet, lock screen, unlock, share screen, dismiss
keygard. Check that no overlay is displayed.

Change-Id: Iad54a91f08cc34db56ea4bbacd894e563ccc3c1e