+增加一个退出Unity时清空队列的功能；

UpmGitExtension/Assets/UpmGitExtension/Editor/Core/PackageTask/PackageInstallQueue.cs

@@ -25,7 +25,10 @@ namespace Cocklebur
             get
             {
                 if (mInstance == null)
+                {
                     mInstance = AssetDatabase.LoadAssetAtPath<PackageInstallQueue>(assetPath);
+                    Application.quitting += OnAppQuit;
+                }
                 return mInstance;
             }
         }
@@ -59,5 +62,10 @@ namespace Cocklebur
             return task;
         }
 
+        /// <summary>
+        /// 退出Unity时清空；
+        /// </summary>
+        private static void OnAppQuit() { mInstance?.Clear(); }
+
     }
 }
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