S3_0 version to be applied to S2_6 too
Maybe those asserts are not overzealous, but they have been detecting an actual bug. They are in the context of units in city.units_supported, so there should NOT be any NoHome units there.
Actual bugfix attached. master & S3_1 affected.
Overzealous asserts in place_unit() and check_city_good() fail for NoHome units.