dtpanel core dump in sparse menus.ini

[MrStevenCarr]

dtpanel core dumps when menus.ini only contains a section.

In void PanelWindow::onFocus(void* caller)

Motif::Color color(menuButtons.at(0)->getHighlightColor());

Should be

Motif::Color color(( menuButtons.size()>0 ? menuButtons.at(0)->getHighlightColor() : getBackground()));

[arcfide]

Can you push a branch that addresses this feature? We can review that branch and then merge it in to the master.