Fix gesture nav after CSD warning dialog is shown.

This CL fixes a gesture navigation bug that would happen right after the
CSD warning dialog was shown and until any other SystemUIDialog would be
shown. See http://b/276821983#comment20 for details.

Bug: 276821983
Test: Manual, cherry-pick http://ag/22573874 and click the Internet tile
      to show the CSD dialog. Swiping up to home from an app should work
      as expected.
Change-Id: Ib238823a9b1d273202ebeded7de21e2f17baa063