fix: constantly write script by sftp

lib/data/model/server/server.dart

@@ -10,7 +10,7 @@ class Server implements TagPickable {
   SSHClient? client;
   ServerState state;
 
-  /// Whether is generating client. 
+  /// Whether is generating client.
   /// Use this to avoid reconnecting if last connect try not finished.
   bool isGenerating = false;
 

lib/data/model/sftp/req.dart

@@ -78,14 +78,12 @@ class SftpReqStatus {
       case int:
         size = event;
         break;
-      case Exception:
-        error = event;
-        break;
       case Duration:
         spentTime = event;
         break;
       default:
-        error = Exception('unknown event: $event');
+        error = Exception('sftp worker event: $event');
+        dispose();
     }
     notifyListeners();
   }