When "Add guest" got tapped multiple times then the first click starts
the guest creation process which blocks the UI thread for around 2-3
seconds, then triggers the open guest details intent, and the second
tap event starts another guest creation, but it fails (since there
can't be more than 1 guest on the device) and returns null, and in the
openUserDetails we get NullPointerException.
Test: manual test
Video: http://shortn/_i4Dce33yhl
Bug: 160267016
Change-Id: I9a4f0a91295e336d246abe5f5470682a14cb510f
57154fbac3