initial usn is 0, so distinguish between 0 and false

anki/decks.py

@@ -163,6 +163,9 @@ class DeckManager(object):
         "A list of all decks."
         return self.decks.values()
 
+    def count(self):
+        return len(self.decks)
+
     def get(self, did, default=True):
         id = str(did)
         if id in self.decks:

anki/sync.py

@@ -565,7 +565,7 @@ class MediaSyncer(object):
             runHook("sync", "streamMedia")
             zip = self.files()
             usn = self.server.addFiles(zip=zip)
-            if usn:
+            if usn is not False:
                 # when server has run out of files, it returns bumped usn
                 break
         # step 5: finalize