Fix crash when cancel open file dialog.

Closes #3232.

src/gui/mainwindow.cpp

@@ -1028,6 +1028,7 @@ void MainWindow::on_actionOpen_triggered()
             QFileDialog::getOpenFileNames(0, tr("Open Torrent Files"), pref->getMainLastDir(),
                                           tr("Torrent Files") + QString::fromUtf8(" (*.torrent)"));
     const bool useTorrentAdditionDialog = Preferences::instance()->useAdditionDialog();
+    if (!pathsList.isEmpty()) {
         foreach (QString file, pathsList) {
             qDebug("Dropped file %s on download list", qPrintable(file));
             if (useTorrentAdditionDialog)
@@ -1040,6 +1041,7 @@ void MainWindow::on_actionOpen_triggered()
         QStringList top_dir = Utils::Fs::fromNativePath(pathsList.at(0)).split("/");
         top_dir.removeLast();
         pref->setMainLastDir(Utils::Fs::fromNativePath(top_dir.join("/")));
+    }
 }
 
 void MainWindow::activate()