Does nothing if extension is empty. The extension check is case
sensitive.

Change-Id: I58f89eb57d53146dae95e58d77cd8b47826b8f42
Reviewed-on: http://codereview.qt-project.org/5163


Reviewed-by: Qt Sanity Bot <qt_sanity_bot@ovi.com>
Reviewed-by: Alessandro Portale <alessandro.portale@nokia.com>