getQueuedBuilds(): Don't catch errors while loading a build from the queue

Dependencies

• [2] TKA75HWS Robustness
• [3] JAUB2FT5 getQueuedBuilds(): Handle dependent builds first
• [*] 24BMQDZA Start of single-process hydra-queue-runner

Change contents

• replacement in src/hydra-queue-runner/hydra-queue-runner.cc at line 722
  [2.76]→[2.76:216](∅→∅)
  − printMsg(lvlError, format("while loading build %1%: %2%") % build->id % e.what());

  − continue; // FIXME: retry later?
  [2.76]

  [2.216]
  + e.addPrefix(format("while loading build %1%: ") % build->id);

  + throw;