rfalke: Fix two cases where invalid city coordinates...

This is an automated notification of a change to freeciv cvs, 
on Wed Oct  3 02:16:55 PDT 2001 = Wed Oct  3 09:16:55 2001 (GMT)
by Raimar Falke <rf13@xxxxxxxxxxxxxxxxxxxxxx>

---- Files affected:

freeciv/client packhand.c
freeciv/client/gui-gtk citydlg.c
freeciv/common city.c
freeciv/server savegame.c

---- Log message:

Fix two cases where invalid city coordinates are passed to
base_city_map_to_map. Fix GTK client city dialog drawing of the corner
tiles.

Reported by Gaute B Strokkenes <gs234@xxxxxxxxx> as (PR#986). Patch be
me.