hydra-queue-runner: Fix handling of missing derivations

Dependencies

• [2] TPNHTE5V Remove obsolete Builds columns and provide accurate "Running builds"
• [3] MHVIT4JY Split hydra-queue-runner.cc more
• [4] 73YR46NJ hydra-queue-runner: Write directly to a binary cache
• [5] VQISTKOP hydra-queue-runner: Use substitutes
• [6] BRAESISH Warn if PostgreSQL appears stalled

Change contents

• replacement in src/hydra-queue-runner/queue-monitor.cc at line 130
  [3.23444]→[2.359:509](∅→∅)
  − ("update Builds set finished = 1, buildStatus = $2, startTime = $3, stopTime = $3, errorMsg = $4 where id = $1 and finished = 0")
  [3.23444]

  [3.23604]
  + ("update Builds set finished = 1, buildStatus = $2, startTime = $3, stopTime = $3 where id = $1 and finished = 0")
• replacement in src/hydra-queue-runner/queue-monitor.cc at line 133
  [3.23674]→[3.23674:23784](∅→∅)
  − (time(0))

  − ("derivation was garbage-collected prior to build").exec();
  [3.23674]

  [3.23784]
  + (time(0)).exec();