Fix random HTTP 404 when viewing build details

Added a unit test (and supporting localExpiredBuilder) to expose a
defect in the search() method of AbstractLazyLoadRunMap whereby the
index contained an entry for the requested build number, but the
BuildReference's referent was null.
Fixed the search() method to handle this rare[ish] corner case.
Minor formatting fixes.
Merge pull request #928 from olivierdagenais/FixRandomHttp404

[FIXED JENKINS-19418] Fix random HTTP 404 when viewing build details