Git: Use indexes to address pretty printing combobox

This fixes a incompatibility with the config settings.

Change-Id: I518291af2309acfaba7eea78b22519c283114009
Reviewed-on: http://codereview.qt-project.org/6161


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