Test update:
1. Start 3 seats: seat0 (login user0), seat1 (login user1), seat2 (login user2)
2. seat0 user0 logout. All is ok. gdm greeter respawn as expected.
Than can login again with user0.
3. seat1 user1 logout. greeter respawn on seat 0. seat1 screen is blank.
greeter from seat1 respawn on seat0 (can be accessed with
ctrl+alt+f9 from seat0)
user0 session is steel active and can be accessed by pressing ctrl+alt+f8