Fix; Skip adding a `parent_sha` if the `parent_sha` has not been benchmarked ever#2255

Kobzol merged 2 commits intorust-lang:masterrust-lang/rustc-perf:masterfrom

Jamesbarford:fix/parent-request-job-queuingJamesbarford/rustc-perf:fix/parent-request-job-queuingCopy head branch name to clipboard