BuildDiff: ensure buildstatus is defined

Dependencies

• [2] NYIIFA32 BuildDiff: split out from JobsetEval GET impl
• [3] ZAISBSNH BuildDiff: cleanup imports and make slightly more readable

Change contents

• replacement in src/lib/Hydra/Helper/BuildDiff.pm at line 74
  [2.2183]→[2.2183:2223](∅→∅)
  − if ($build->buildstatus != 0) {
  [2.2183]

  [2.2223]
  + if (defined $build->buildstatus && $build->buildstatus != 0) {