fix gitserver error aggregation and stop swallowing search errors

Created by: camdencheek

This fixes error aggregation in gitserver so searches without errors don't return a "zero errors found" error. It also adds a log at a place where we were previously swallowing an error.

Thread: https://sourcegraph.slack.com/archives/CMBA8F926/p1636553506165900

It's still unclear why this just started happening. I don't see any changes I would have expected to affect this.