Cope with missing schema locations
Cope with missing schema locations

jonfoster/pyxb-upstream-mirror,balanced/PyXB,jonfoster/pyxb2,jonfoster/pyxb1,CantemoInternal/pyxb,pabigot/pyxb,jonfoster/pyxb-upstream-mirror,jonfoster/pyxb2,jonfoster/pyxb1,pabigot/pyxb,CantemoInternal/pyxb,balanced/PyXB,jonfoster/pyxb2,jonfoster/pyxb-upstream-mirror,CantemoInternal/pyxb,balanced/PyXB