dev/sg: fix nil reference on build author
Created by: bobheadxi
Closes https://github.com/sourcegraph/sourcegraph/issues/36239
Also inspires https://github.com/sourcegraph/sourcegraph/pull/36256
Test plan
n/a, I just read the stacktrace and fixed the exact nil pointer that was encountered - couldn't reproduce locally (might have hit a custom build triggered via API)