Freeciv

Currently access_areas_refresh() iterates tiledef checks up to MAX_TILEDEFS. It should check only actually existing tiledefs. Just use tiledef_iterate() which will do the right thing in this respect too.
While at it, also change pf iteration loop to be the outer one and tiledef iteration loop the inner one for slight performance boost (tiledef iteration is quicker one to run over and over again).