tracker: remove typo from previous patch

tracker/automated/test-tracker.py

@@ -148,7 +148,7 @@ class TrackerTest(unittest.TestCase):
         self.loop.run()
 
         context = self.loop.get_context()
-        while len(self.tumbler_queue) >= 0:
+        while len(self.tumbler_queue) > 0:
             context.iteration(False)
 
         self.assert_has_thumbnail('Documents/lorem_presentation.odp')