Fixing a bug in diff, where some changes were ignored for no reason

Dependencies

• [2] SXEYMYF7 Fixing the bad changes in history (unfortunately, by rebooting).

Change contents

• replacement in libpijul/src/diff/replace.rs at line 84
  [2.782799]→[2.782799:782823](∅→∅)
  − _ => {}
  [2.782799]

  [2.782823]
  + None => {}