Fix cancel operation for example "Application"

On the save dialog the cancel option is detected now from exec()
method.

Change-Id: I977626b83fe770ddc148b57551becd04e5fd9dd5
Task-number: QTBUG-41020
Reviewed-by: Alessandro Portale <alessandro.portale@digia.com>

examples/widgets/mainwindows/application/mainwindow.cpp

@@ -121,10 +121,10 @@ bool MainWindow::saveAs()
     QFileDialog dialog(this);
     dialog.setWindowModality(Qt::WindowModal);
     dialog.setAcceptMode(QFileDialog::AcceptSave);
-    dialog.exec();
-    QStringList files = dialog.selectedFiles();
-
-    if (files.isEmpty())
+    QStringList files;
+    if (dialog.exec())
+        files = dialog.selectedFiles();
+    else
         return false;
 
     return saveFile(files.at(0));