Fix an issue with custom policy edit control not populating correctly

Summary: These values aren't always provided. They should be, but just make things work for now.

Test Plan:

• Edited a task.
• Selected "Custom Policy" for "Edit Policy".
• Configured a policy like "Users: dog".
• Saved policy.
• Selected "Custom Policy" again to edit the policy.
• Before patch: tokenizer fails to render with an error (config.types is not an object).
• After patch: tokenizer renders properly, albeit with a missing icon.

Reviewers: btrahan, chad

Reviewed By: chad

Subscribers: epriestley

Differential Revision: https://secure.phabricator.com/D12477