[18Ardennes] Fix error on tokening multi-slot city

An error was occurring when attempting to token the brown Ruhr tile
(3-slot city). There was already a token in slot #0. If the player
clicks on slot #1 when placing a token this worked correctly, but
clicking on slot #2 errored, as the game was then attempting to change
the logo of the token in slot #2, but the token had gone to slot #1.

Fixes #133.

lib/engine/game/g_18_ardennes/step/token.rb

@@ -73,13 +73,12 @@ def process_remove_token(action)
           end
 
           def process_place_token(action)
-            entity = action.entity
-            city = action.city
-            slot = action.slot
+            super
 
+            city = action.city
+            slot = city.tokens.index(action.token)
             city.slot_icons.delete(slot)
-            super
-            @game.change_token_icon(city, city.tokens[slot], entity)
+            @game.change_token_icon(city, action.token, action.entity)
           end
         end
       end