WC: Fix schema validation

When one attribute is dependent on another, apparently order matters.

data/campaigns/World_Conquest/scenarios/WC_II_scenario.cfg

@@ -38,7 +38,6 @@ _ "World Conquest 3p" #enddef
         [generator]
             id="WC_II_{PLAYERS}p"
             config_name={WC_II_CAMPAIGN_NAME_{PLAYERS}P}
-            nplayers={PLAYERS}
             create_scenario = <<
                 local a = ...
                 local function doit()
@@ -71,6 +70,8 @@ _ "World Conquest 3p" #enddef
                 end
             >>
 #endif
+            nplayers={PLAYERS}
+            foo=bar
             [scenario]
                 {DEFAULT_SCHEDULE}
                 {DEFAULT_MUSIC_PLAYLIST}