Bug fix: Late crash when closing Creator while building debugging helper (QTCREATORBUG-1576).

Reviewed-by: hjk

src/plugins/coreplugin/coreimpl.cpp

@@ -61,6 +61,11 @@ CoreImpl::CoreImpl(MainWindow *mainwindow)
     m_mainwindow = mainwindow;
 }
 
+CoreImpl::~CoreImpl()
+{
+    m_instance = 0;
+}
+
 QStringList CoreImpl::showNewItemDialog(const QString &title,
                                         const QList<IWizard *> &wizards,
                                         const QString &defaultLocation)

src/plugins/coreplugin/coreimpl.h

@@ -42,7 +42,7 @@ class CoreImpl : public ICore
 
 public:
     CoreImpl(MainWindow *mainwindow);
-    ~CoreImpl() {}
+    ~CoreImpl();
 
     QStringList showNewItemDialog(const QString &title,
                                   const QList<IWizard *> &wizards,

src/plugins/projectexplorer/debugginghelper.cpp

@@ -113,6 +113,8 @@ QStringList DebuggingHelperLibrary::debuggingHelperLibraryLocationsByInstallData
 
 QString DebuggingHelperLibrary::debuggingHelperLibraryByInstallData(const QString &qtInstallData)
 {
+    if (!Core::ICore::instance())
+        return QString();
     const QString dumperSourcePath = Core::ICore::instance()->resourcePath() + QLatin1String("/gdbmacros/");
     QDateTime lastModified = QFileInfo(dumperSourcePath + "gdbmacros.cpp").lastModified();
     // We pretend that the lastmodified of gdbmacros.cpp is 5 minutes before what the file system says