修复再Free过程中系统退出时的bug

GcDevicePc/MDIBase.cs

@@ -424,12 +424,16 @@ namespace GcDevicePc
         }
 
         private void WaitHMIFree()
+        {
+            if (!backgroundWorker1.IsBusy)
             {
                 this.workProgress.Visible = true;
                 this.workProgress.Value = 0;
                 this.backgroundWorker1.RunWorkerAsync();
             }
            
+        }
+
         private void backgroundWorker2_DoWork(object sender, DoWorkEventArgs e)
         {
             int ret = -1;