Fix two diff rendering bugs

Summary:
  - The order of operations for file changes is wrong. We need to wrap them in a table, then render the changeset talbe around that table.
  - Line data was being set to late, so renderShield() got the wrong line count and rendered empty diffs behind, e.g., generated changes.

Test Plan: Looked at an image change with property changes. Clicked "show file contents" on a generated file.

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T2009

Differential Revision: https://secure.phabricator.com/D4432