Fix crash with adding catalogs in the launcher

Change how we get notified about catalog changes, so we can remove
our hook and hence not leave a dangling pointer.

Fixes https://sourceforge.net/p/flightgear/codetickets/1994/

src/GUI/AddCatalogDialog.cxx

@@ -30,6 +30,23 @@
 
 using namespace simgear::pkg;
 
+class AddCatalogDialog::AddCatalogDelegate : public simgear::pkg::Delegate
+{
+public:
+    AddCatalogDelegate(AddCatalogDialog* outer) : p(outer) {}
+    
+    void catalogRefreshed(CatalogRef catalog, StatusCode) override
+    {
+        p->onCatalogStatusChanged(catalog);
+    }
+
+    void startInstall(InstallRef) override {}
+    void installProgress(InstallRef, unsigned int, unsigned int) override {}
+    void finishInstall(InstallRef, StatusCode ) override {}
+private:
+    AddCatalogDialog* p = nullptr;
+};
+
 AddCatalogDialog::AddCatalogDialog(QWidget *parent, RootRef root) :
     QDialog(parent, Qt::Dialog
                     | Qt::CustomizeWindowHint
@@ -37,7 +54,6 @@ AddCatalogDialog::AddCatalogDialog(QWidget *parent, RootRef root) :
                     | Qt::WindowSystemMenuHint
                     | Qt::WindowContextHelpButtonHint
                     | Qt::MSWindowsFixedSizeDialogHint),
-    m_state(STATE_START),
     ui(new Ui::AddCatalogDialog),
     m_packageRoot(root)
 {
@@ -51,6 +67,9 @@ AddCatalogDialog::AddCatalogDialog(QWidget *parent, RootRef root) :
 
 AddCatalogDialog::~AddCatalogDialog()
 {
+    if (m_delegate) {
+        m_packageRoot->removeDelegate(m_delegate.get());
+    }
     delete ui;
 }
 
@@ -137,8 +156,9 @@ void AddCatalogDialog::startDownload()
 {
     Q_ASSERT(m_catalogUrl.isValid());
 
+    m_delegate.reset(new AddCatalogDelegate{this});
+    m_packageRoot->addDelegate(m_delegate.get());
     m_result = Catalog::createFromUrl(m_packageRoot, m_catalogUrl.toString().toStdString());
-    m_result->addStatusCallback(this, &AddCatalogDialog::onCatalogStatusChanged);
     m_state = STATE_DOWNLOADING;
     updateUi();
     ui->stack->setCurrentIndex(STATE_DOWNLOADING);
@@ -175,6 +195,10 @@ void AddCatalogDialog::reject()
 
 void AddCatalogDialog::onCatalogStatusChanged(Catalog* cat)
 {
+    if (cat != m_result) {
+        return;
+    }
+    
     Delegate::StatusCode s = cat->status();
     switch (s) {
     case Delegate::STATUS_REFRESHED:

src/GUI/AddCatalogDialog.hxx

@@ -21,6 +21,8 @@
 #ifndef FG_GUI_ADDCATALOGDIALOG_HXX
 #define FG_GUI_ADDCATALOGDIALOG_HXX
 
+#include <memory>
+
 #include <QDialog>
 #include <QUrl>
 
@@ -31,6 +33,7 @@ namespace Ui {
 class AddCatalogDialog;
 }
 
+
 class AddCatalogDialog : public QDialog
 {
     Q_OBJECT
@@ -56,10 +59,12 @@ private slots:
 
     void onUrlTextChanged();
 private:
+    class AddCatalogDelegate;
+    friend class AddCatalogDelegate;
+
     void startDownload();
     void updateUi();
 
-    // callback from the catalog
     void onCatalogStatusChanged(simgear::pkg::Catalog* cat);
 
     enum State {
@@ -70,13 +75,15 @@ private:
 
     };
 
-    State m_state;
+    State m_state = STATE_START;
 
     Ui::AddCatalogDialog *ui;
     simgear::pkg::RootRef m_packageRoot;
     QUrl m_catalogUrl;
     simgear::pkg::CatalogRef m_result;
     bool m_nonInteractiveMode = false;
+
+    std::unique_ptr<AddCatalogDelegate> m_delegate;
 };
 
 #endif // FG_GUI_ADDCATALOGDIALOG_HXX