insights: fix nil pointer bug in worker for records with no record_time
Created by: coury-clark
Closes https://github.com/sourcegraph/sourcegraph/issues/25131
In scenarios where there is a null record_time we want to default to using the current time. This will enable the behavior that queries using the current index will always correlate to the time they were executed. This fixes a bug where any results that produce a limitHit
would fail with a nil deserialization.