Prevent a division by zero in hydra-queue-runner

Dependencies

• [2] GEADFVZ5 hydra-queue-runner: Improved scheduling
• [3] NREF6YOA * Don't start more builds concurrently than allowed for each system
• [4] 3PNG7NIB Remove trailing whitespace
• [*] 7YBYT2LQ

Change contents

• replacement in src/script/hydra-queue-runner at line 109
  [2.3393]→[2.3393:3440](∅→∅)
  − my $totalShares = getTotalShares($db);
  [2.3393]

  [2.3440]
  + my $totalShares = getTotalShares($db) || 1;