Fix an issue with viewing an empty board with milestone columns

Summary:
Ref T10010.

• Viewing an empty board with milestone columns did a meaningless edge query. Don't do that.
• When creating the first milestone of a parent, force the indexing engine to rematerialize it inline. This sets hasMilestones properly. Otherwise, the daemons may take some time to fix this in the indexer.

Test Plan:

• Viewed an empty board of a project with a milestone.
• Viewed a normal board.
• Created the first milestone of a project with a big queue of daemons, saw project state immediately fully reflect the project having milestones.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T10010

Differential Revision: https://secure.phabricator.com/D15206