[cloud functions] Fix error when a landed CL has no tryjobs
[cloud functions] Fix error when a landed CL has no tryjobs

TBR: 29642742b6693024c89de8232f2e2542cf7eedf7@google.com
Change-Id: If3ac92b797dcf60c3633e318b9a6ea0921b58fe1
Reviewed-on: https://dart-review.googlesource.com/c/dart_ci/+/131862
Reviewed-by: William Hesse <a821cddceae7dc400f272e3cb1a72f400f9fed6d@google.com>

dart-lang/dart_ci,dart-lang/dart_ci,dart-lang/dart_ci,dart-lang/dart_ci