xorg.mxfontscale: Fix segfault with some fonts.

The update to version 1.1.2 in 9c22c1b3 introduces a segfault when
mkfontscale is processing fonts where the family name is missing.

Applies a patch from Stefan Dirsch <sndirsch@suse.com> to be found at:

https://bugs.freedesktop.org/show_bug.cgi?id=89409



Signed-off-by: aszlig <aszlig@redmoonstudios.org>