Clears search view focus when returning from result list.

Done via posted `Runnable` since `Activity#onResumed()` automatically re-assigns focus to first focusable view (search).

* `PagerResultsFragment#onResume()` posts a `Runnable` to clear search view focus.
* Prevents NPE in `BaseActivity#getSearchView()` when `menuItem` has not yet been initialized.
* Renames `menuItem` -> `searchMenuItem` and relaxes scope for readability and testability.