Fix memory corruption.
Fix memory corruption.

g_free(c) in the original code was freeing memory at the pointer
that was incremented a few times since the allocation.

This is similar to ubuntu bug #899290 and fedora bug 589898.

igors/xfce4-xkb-plugin,igors/xfce4-xkb-plugin,igors/xfce4-xkb-plugin