Fix NPE when restarting ChooseTypeAndAccountActiivty.

Note that this change still leaves things in an imperfect state. Now instead
of ANR with an NPE it will reshow the Choose account activity and then on the
second back, it will go away. So the user isn't hosed. But it is still a sloppy
experience.  Basically the bug fix reveals another not quite as bad bug
(see https://b/8661942).

Bug: 8151602
Change-Id: I44b188f5940d464c2dd81dd0b6b7cae3c189becd