Fix a fatal when navigating to a Workboard after removing the Workboard menu item
See PHI1247. If you remove the Workboard from a project profile menu, then navigate to the URI, we currently fatal when trying to select the "Workboard" item.
Instead, only try to select the item if some matching item is present.
- Disabled the workboard on a project, navigated to /board/, got a sensible page with no navigation item selected instead of a fatal.
- Viewed a normal workboard, saw the correct selection.
Reviewed By: amckinley
Differential Revision: https://secure.phabricator.com/D20516