Do None check before isinstance check.

voussoirkit/spinal.py

@@ -685,12 +685,12 @@ def limiter_or_none(value):
     Returns a Ratelimiter object if the argument can be normalized to one,
     or None if the argument is None. Saves the caller from having to if.
     '''
-    if isinstance(value, ratelimiter.Ratelimiter):
-        return value
-
     if value is None:
         return None
 
+    if isinstance(value, ratelimiter.Ratelimiter):
+        return value
+
     if isinstance(value, str):
         value = bytestring.parsebytes(value)