bitbake: runqueue: Fix handling of zero priority task

The zero priority task should be run first but was being confused with
the None value the priority field defaulted to. Check for None
explicitly to avoid this error.

In the real world this doesn't change much but it confused the debug
output from the schedulers.

(Bitbake rev: 49c9d8c9400f74c804c2f36462639236e0841ff0)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

bitbake/lib/bb/runqueue.py

@@ -139,7 +139,7 @@ class RunQueueScheduler(object):
         bestprio = None
         for taskid in self.buildable:
             prio = self.rev_prio_map[taskid]
-            if not bestprio or bestprio > prio:
+            if bestprio is None or bestprio > prio:
                 stamp = self.stamps[taskid]
                 if stamp in self.rq.build_stamps.itervalues():
                     continue