Fixing missing movement bounds notification to SystemUI.

- When WM updates from a configuration change, ensure that we update the
  pinned stack controller even if there is currently no pinned stack.
- Also finish the menu activity once an activity is unpinned.

Bug: 36879891
Test: android.server.cts.ActivityManagerPinnedStackTests
Change-Id: I789945c1783693cf4b4e3d6663548c8669784001