altosui: Don't display 0000-00-00 for missing flight log dates

[fw/altos] / debian / menu

?package(altos): \
        needs="X11" \
        section="Applications/Viewers" \
        title="ao-view" \
        command="/usr/bin/ao-view" \
        icon="/usr/share/pixmaps/altusmetrum.xpm"