fix(outbound): return early if there are no messages to be sent

shiftregister/messaging/outbound.py

@@ -31,10 +31,13 @@ def send(messages):
     else:
         messages = list(messages)
 
+    if len(messages) == 0:
+        return
+
     sent_messages = 0
     for message in sender.send(messages):
         sent_messages += 1
         yield message
 
-    if sent_messages == 0 and len(messages) > 0:
+    if sent_messages == 0:
         raise OutboundMessageError("no messages have been sent")