Fixing a couple nav bar crashes

- Reset the rotation button controller callback when detaching the nav
  bar (the callback can otherwise be called back)
- Only touch autohide if the controller is set (RotationButtonController
  update callback is set when initialized and not unset, so it too can
  callback into the nav bar view after it's been destroyed)
- Add workaround for issue where content provider can still callback
  the observer after the observer has been unregistered, but the msg
  has been posted to the handler (filed b/198002034 to track fw fix)

Bug: 194631201
Bug: 183051107
Bug: 197946101
Test: atest SystemUITests
Change-Id: I520ca261b012d1d7f04ea8f732819e7eb1b4f77f