Do not leave the Options Interfaces Dialog open, when the Main Window is closed.

Change-Id: Ifd4fb88ceff24561131fad1d72531889e323f5ac
Reviewed-on: https://code.wireshark.org/review/1651
Reviewed-by: Anders Broman <a.broman58@gmail.com>

ui/qt/main_window.cpp

@@ -409,6 +409,7 @@ void MainWindow::closeEvent(QCloseEvent *event) {
         return;
     }
 
+    capture_interfaces_dialog_.close();
     // Make sure we kill any open dumpcap processes.
     delete main_welcome_;