Move check for enabled MDNs from message rendering to MDN job

src/job.rs

@@ -255,9 +255,14 @@ impl Job {
 
     #[allow(non_snake_case)]
     fn SendMdn(&mut self, context: &Context) -> Status {
+        if !context.get_config_bool(Config::MdnsEnabled) {
+            // User has disabled MDNs after job scheduling but before
+            // execution.
+            return Status::Finished(Err(format_err!("MDNs are disabled")));
+        }
+
         let msg_id = MsgId::new(self.foreign_id);
         let msg = job_try!(Message::load_from_db(context, msg_id));
-
         let mimefactory = job_try!(MimeFactory::from_mdn(context, &msg));
         let rendered_msg = job_try!(mimefactory.render());
         let body = rendered_msg.message;

src/mimefactory.rs

@@ -159,13 +159,6 @@ impl<'a, 'b> MimeFactory<'a, 'b> {
     }
 
     pub fn from_mdn(context: &'a Context, msg: &'b Message) -> Result<Self, Error> {
-        // MDNs not enabled - check this is late, in the job. the
-        // user may have changed its choice while offline ...
-        ensure!(
-            context.get_config_bool(Config::MdnsEnabled),
-            "MDNs meanwhile disabled"
-        );
-
         let contact = Contact::load_from_db(context, msg.from_id)?;
 
         // Do not send MDNs trash etc.; chats.blocked is already checked by the caller