- Correct dkim.verify processing to avoid errors when verifying messages

with no DKIM signatures

dkim/__init__.py

@@ -934,8 +934,11 @@ class DKIM(DomainSigner):
   #: @return: True if signature verifies or False otherwise
   #: @raise DKIMException: when the message, signature, or key are badly formed
   def verify(self,idx=0,dnsfunc=get_txt):
-    sig, include_headers, sigheaders = self.verify_headerprep(idx)
-    return self.verify_sig(sig, include_headers, sigheaders[idx], dnsfunc)
+    prep = self.verify_headerprep(idx)
+    if prep:
+        sig, include_headers, sigheaders = prep
+        return self.verify_sig(sig, include_headers, sigheaders[idx], dnsfunc)
+    return False # No signature
 
 
 #: Hold messages and options during ARC signing and verification.