enhance: do not start new auto-fetch action if the last one is still running (#2285)

Signed-off-by: leo <longshuang@msn.cn>

Author: love-linger

src/ViewModels/Repository.cs

@@ -1865,7 +1865,7 @@ private void AutoFetchByTimer(object sender)
 
         private async Task AutoFetchOnUIThread()
         {
-            if (_uiStates == null)
+            if (IsAutoFetching)
                 return;
 
             CommandLog log = null;