fix: prevent crash on exit by using non-creating singleton accessor

src/editorapplication.cpp

@@ -1,4 +1,4 @@
-// SPDX-FileCopyrightText: 2019 - 2022 UnionTech Software Technology Co., Ltd.
+// SPDX-FileCopyrightText: 2019-2026 UnionTech Software Technology Co., Ltd.
 //
 // SPDX-License-Identifier: GPL-3.0-or-later
 
@@ -46,9 +46,9 @@ EditorApplication::~EditorApplication()
 {
     qDebug() << "Enter EditorApplication destructor";
     // app结束时，释放
-    if (nullptr != StartManager::instance()) {
+    if (nullptr != StartManager::instanceOrNull()) {
         qDebug() << "Deleting StartManager instance";
-        delete StartManager::instance();
+        delete StartManager::instanceOrNull();
     } else {
         qDebug() << "StartManager instance is already null";
     }

src/startmanager.cpp

@@ -42,6 +42,11 @@ StartManager *StartManager::instance()
     return m_instance;
 }
 
+StartManager *StartManager::instanceOrNull()
+{
+    return m_instance;
+}
+
 StartManager::~StartManager()
 {
     qDebug() << "Enter StartManager destructor";

src/startmanager.h

@@ -30,6 +30,7 @@ class StartManager : public QObject
     };
 
     static StartManager *instance();
+    static StartManager *instanceOrNull();
     explicit StartManager(QObject *parent = nullptr);
     ~StartManager();
     bool checkPath(const QString &file);