Return earlier when validate_signatures is turned off

When connecting to a bus without messages being signed, an exception would be raised with the message "Topic envelope mismatch". If signing is turned off, none of the message c
ontents should be examined in the `validate` function.

fedmsg/consumers/__init__.py

@@ -204,6 +204,10 @@ def _make_query(page=1):
 
     def validate(self, message):
         """ This needs to raise an exception, caught by moksha. """
+        # If we're not validating, then everything is valid.
+        # If this is turned on globally, our child class can override it.
+        if not self.validate_signatures:
+            return
 
         if hasattr(message, '__json__'):
             message = message.__json__()
@@ -214,11 +218,6 @@ def validate(self, message):
         if not message['topic'] == message['body']['topic']:
             raise RuntimeWarning("Topic envelope mismatch.")
 
-        # If we're not validating, then everything is valid.
-        # If this is turned on globally, our child class can override it.
-        if not self.validate_signatures:
-            return
-
         if not fedmsg.crypto.validate(message['body'], **self.hub.config):
             raise RuntimeWarning("Failed to authn message.")