Do not start RecentsMixedTransition if keyguard transition is playing

If the keyguard transition animation is playing before/during start
recents transition, there should not start recents mixed transition
because recents won't receive keyguard transition, which would cause
recents get stucked.
Also just fallback to normal recents transition if the keyguard state
was changed when RecentsMixedTransition receive transition ready.

Flag: EXEMPT bugfix
Bug: 378002568
Test: try to simulate by launch app from keyguard-shortcut, unlock
keyguard with face unlock, and trigger recents at the same time.

Change-Id: I28d6fbfdf5f47548ceb7ffdcc47b57866a8e14a5