ndfd: work around inconsistency in amount of data returned
ndfd: work around inconsistency in amount of data returned

This morning the NDFD is returning only two days for maximum (daytime)
temperature estimates, but six days for minimum (nighttime) temperature
estimates.  Odd.

OK, they fixed whatever they did, but I'm leaving this here.

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