make ExponentialRetryTimeout.seconds_to_wait always return an int

src/authentic2/exponential_retry_timeout.py

@@ -52,12 +52,12 @@ class ExponentialRetryTimeout(object):
            done.
         '''
         key = self.key(keys)
-        if not self.duration:
-            return 0
-        now = time.time()
-        what = cache.get(key)
-        if what and what[1] > now:
-            return what[1] - now
+        if self.duration:
+            now = time.time()
+            what = cache.get(key)
+            if what and what[1] > now:
+                return what[1] - now
+        return 0
 
     def success(self, *keys):
         '''Signal an action success, delete exponential backoff cache.