Get rid of the aerc.PushError(" " + $string) idiom

The individual callers should not be responsible for padding

commands/msg/read.go

@@ -187,7 +187,7 @@ func submitFlagChange(aerc *widgets.Aerc, store *lib.MessageStore,
 		case *types.Done:
 			wg.Done()
 		case *types.Error:
-			aerc.PushError(" " + msg.Error.Error())
+			aerc.PushError(msg.Error.Error())
 			*success = false
 			wg.Done()
 		}