Show "Show Older" for transactions the user has not interacted with

Summary: Fixes T7454. We weren't triggering "Show Older" unless there were hidden events because of a previous interaction.

Test Plan:

• Set page size to 3.
• Viewed a task with ~10 transactions.
• Before patch:
  • Only 3 most recent transactions visible, no way to see older ones.
  • Saw "show older" appear, paged backward through transaction histroy.
• Also, interacted with task and then viewed it, made sure "show older" still works.

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T7454

Differential Revision: https://secure.phabricator.com/D11963