Workaround for buildbot#601, when a build is locked it may not be in …

…currentBui

lds, but also not in the cache or on disk. In that case, the BuilderStatus eventGenerator ends up not returning any builds.
 - I'm not sure of the correct fix, so just ignore failures looking up the most
   recent build.

buildbot/status/builder.py

@@ -1737,6 +1737,11 @@ def eventGenerator(self, branches=[], categories=[]):
         for Nb in range(1, self.nextBuildNumber+1):
             b = self.getBuild(-Nb)
             if not b:
+                # HACK: If this is the first build we are looking at, it is
+                # possible it's in progress but locked before it has written a
+                # pickle; in this case keep looking.
+                if Nb == 1:
+                    continue
                 break
             if branches and not b.getSourceStamp().branch in branches:
                 continue