Fix definition of evac center.

Somehow the mapping of "1" to "t_window_boarded" has been lost.
It was not reported by the game because "fill_ter" was set and used instead.
That means all the boarded up windows appeared as t_floor instead.
FEMA camp: create t_dirt floor, not t_dirtfloor

t_dirt is outside, whereas t_dirtfloor is an inside terrain.