Check for presence of any Columns before triggering initialization of Workboard

Summary: Ref T6256, this prevents more installs from getting in this weird state. We'll have to follow up if possible to "fix" the issue retroactively.

Test Plan: Test moving a backlog column to new position, hiding rest of other panels.

Reviewers: btrahan, epriestley

Reviewed By: epriestley

Subscribers: Korvin, epriestley

Maniphest Tasks: T6256

Differential Revision: https://secure.phabricator.com/D10651