Core: Wrap moribund dialogs into QPointer

There's no guarantee that items in the collected list don't die for
other reasons before it's their turn in the loop.

Change-Id: I5e81a25c3c205646eece30d6dd1a95f4b97eda05
Reviewed-by: Eike Ziller <eike.ziller@qt.io>

src/plugins/coreplugin/icore.cpp

@@ -2189,16 +2189,18 @@ void ICorePrivate::openFileFromDevice()
 static void acceptModalDialogs()
 {
     const QWidgetList topLevels = QApplication::topLevelWidgets();
-    QList<QDialog *> dialogsToClose;
+    QList<QPointer<QDialog>> dialogsToClose;
     for (QWidget *topLevel : topLevels) {
         if (auto dialog = qobject_cast<QDialog *>(topLevel)) {
             if (dialog->isModal())
                 dialogsToClose.append(dialog);
         }
     }
-    for (QDialog *dialog : dialogsToClose)
+    for (QDialog *dialog : dialogsToClose) {
+        if (dialog)
             dialog->accept();
     }
+}
 
 } // Internal