Support returning 0 from RunConfiguration::createConfigurationWidget

The android plugin does so.

Change-Id: If5e5216bbcb6ba3dcd4186ae4c558efe4d56dcb8
Reviewed-on: http://codereview.qt-project.org/4882


Reviewed-by: Qt Sanity Bot <qt_sanity_bot@ovi.com>
Reviewed-by: Daniel Teske <daniel.teske@nokia.com>