Only search for palette definitions on the world actor

OpenRA.Mods.Common/Lint/CheckPalettes.cs

@@ -121,9 +121,9 @@ namespace OpenRA.Mods.Common.Lint
 
 		void GetPalettes(Ruleset rules, List<string> palettes, List<string> playerPalettes)
 		{
-			foreach (var actorInfo in rules.Actors)
-			{
-				foreach (var traitInfo in actorInfo.Value.TraitInfos<TraitInfo>())
+			// Palettes are only defined on the world actor
+			var worldActorInfo = rules.Actors[SystemActors.World];
+			foreach (var traitInfo in worldActorInfo.TraitInfos<TraitInfo>())
 			{
 				var fields = traitInfo.GetType().GetFields();
 				foreach (var field in fields)
@@ -144,5 +144,4 @@ namespace OpenRA.Mods.Common.Lint
 			}
 		}
 	}
-	}
 }