lint check player palette reference

and tell which actor is affected when a problem is found

OpenRA.Mods.Common/Traits/Render/WithDockingOverlay.cs

@@ -24,7 +24,7 @@ namespace OpenRA.Mods.Common.Traits
 		public readonly WVec Offset = WVec.Zero;
 
 		[Desc("Custom palette name")]
-		public readonly string Palette = null;
+		[PaletteReference("IsPlayerPalette")] public readonly string Palette = null;
 
 		[Desc("Custom palette is a player palette BaseName")]
 		public readonly bool IsPlayerPalette = false;