Don't hide action lists if there are no property list properties

Summary:
Fixes T5108. If we render a property list with no properties, it doesn't render anything. This hides any attached action list.

Instead, insert an empty property if we have an action list but no properties.

(This could use some cleanup eventually, but resolve the issue for now.)

Test Plan: Viewed a property list with actions but no properties; saw actions.

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T5108

Differential Revision: https://secure.phabricator.com/D9201