Only update bar.total when bar is instantiated

The `self.bar.total = total` is called even when `self.bar` is not instantiated.  This results in crash.

lieer/gmailieer.py

@@ -857,7 +857,8 @@ def full_pull(self):
                 previous = self.load_resume(resume_file, last_id)
 
         for total, gids in self.remote.all_messages():
-            self.bar.total = total
+            if not self.args.quiet and self.bar:
+                self.bar.total = total
             self.bar_update(len(gids))
 
             message_gids.extend(m["id"] for m in gids)