datasync: Run only once if interval is zero or negative

datasync.py

@@ -137,6 +137,8 @@ def tick(interval):
     while True:
         t = time.time()
         yield t
+        if interval <= 0.0:
+            break
         tnext += interval
         tsleep = max(0.0, tnext - time.time())
         time.sleep(tsleep)