Fix an issue where pastes could be reordered as a side effect of cache fills

Summary: Ref T7803. Pastes which needed a cache fill would incorrectly be dropped to the bottom of the list. Stop doing that.

Test Plan: Loaded a list of pastes with some that needed cache fills, saw them appear in the correct order.

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T7803

Differential Revision: https://secure.phabricator.com/D12354