[Freeciv-Dev] (PR#14164) gui-win32: audit game.player_ptr users

["Jason Short" <jdorje@xxxxxxxxxxxxxxxxxxxxx>]

<URL: http://bugs.freeciv.org/Ticket/Display.html?id=14164 >

All users of game.player_ptr must be checked.  Now with observers this 
value will be NULL at the client.  There are two posible fixes:

1.  Replace it.  When looking at a unit or city, use punit->owner instead.

2.  Special-case it.  A specific check for NULL should make it easy to 
have a separate case.

-jason