Avoid assignment in if

lib/gitlab/email/receiver.rb

@@ -28,8 +28,9 @@ module Gitlab
         mail = build_mail
         mail_key = extract_mail_key(mail)
-        if handler = Handler.for(mail, mail_key)
+        handler = Handler.for(mail, mail_key)
+        if handler
           handler.execute
         else
           raise UnknownIncomingEmail