[infra] Fix compare_results non-human output being null.
[infra] Fix compare_results non-human output being null.

TBR=whesse@google.com

Change-Id: I8a028bac9fac4200c8fe49249f8ba43d4dd8964e
Reviewed-on: https://dart-review.googlesource.com/c/86207
Reviewed-by: Jonas Termansen <092ec58085ae5e368bc39d18752740ff81a2d09c@google.com>

dartino/dart-sdk,dart-lang/sdk,dart-archive/dart-sdk,dart-lang/sdk,dart-lang/sdk,dartino/dart-sdk,dart-lang/sdk,dart-archive/dart-sdk,dart-archive/dart-sdk,dart-archive/dart-sdk,dart-archive/dart-sdk,dartino/dart-sdk,dart-lang/sdk,dart-archive/dart-sdk,dartino/dart-sdk,dart-lang/sdk,dart-archive/dart-sdk,dart-lang/sdk,dartino/dart-sdk,dartino/dart-sdk,dartino/dart-sdk,dart-lang/sdk,dart-archive/dart-sdk,dart-archive/dart-sdk,dartino/dart-sdk,dartino/dart-sdk