Fix case where we were still handling broadcasts while switching bars

- We reset the nav bar reference after the view is destroyed while
  being recreated, and we don't actually need to update the old
  bar

Bug: 162213184
Test: Switch users and verify we don't handle broadcast while
      there is no nav bar
Change-Id: Ibe1bc0c04d4bb653aaca0b5f51485aeca4f80441