[Freeciv-Dev] (PR#11077) mapview citymap overlays are inefficient

["Jason Short" <jdorje@xxxxxxxxxxxxxxxxxxxxx>]

<URL: http://rt.freeciv.org/Ticket/Display.html?id=11077 >

The mapview draws citymap overlays when you press 't'.  These are 
updated whenever any drawing is done.  However this is inefficient 
because it must search outward to find any cities within radius.  This 
is easy enough when there are only 21 tiles within range, but when there 
are 20,000 tiles it becomes a bit slow ;-).  The thing is this would be 
easy to avoid if we just cached the value.

jason