Disable dialog exit animation when locking (1/2)

Before this CL, when an animated dialog was dismissed because we were
locking the device, we would run the exit animation while fading out the
dialog window with the current doze amount. This did not look really
good.

This CL now disables the exit animation when the dialog is dismissed
because the device was locked.

See b/193634619#comment8 for before/after videos.

Bug: 193634619
Test: Manual
Change-Id: I516b5c0e9ccf9d5650b5708350472aeb209d71e5