Fixing alive vertex detection in down contexts too

Dependencies

• [2] YN63NUZO Sanakirja 1.0
• [3] SXEYMYF7 Fixing the bad changes in history (unfortunately, by rebooting).

Change contents

• replacement in libpijul/src/find_alive.rs at line 26
  [2.134535]→[2.134535:134590](∅→∅)
  − if v.flag().contains(EdgeFlags::BLOCK)
  [2.134535]

  [2.134590]
  + if (v.flag().contains(EdgeFlags::BLOCK) || vertex.is_empty())