Undo an invalid optimisation.

Fixes a regression from #7746.

OpenRA.Game/Traits/Player/FrozenActorLayer.cs

@@ -28,7 +28,7 @@ namespace OpenRA.Traits
 		public readonly WPos CenterPosition;
 		public readonly Rectangle Bounds;
 		readonly Actor actor;
-		readonly Func<MPos, bool> isVisibleTest;
+		readonly Shroud shroud;
 
 		public Player Owner;
 
@@ -45,7 +45,7 @@ namespace OpenRA.Traits
 		public FrozenActor(Actor self, MPos[] footprint, Shroud shroud)
 		{
 			actor = self;
-			isVisibleTest = shroud.IsVisibleTest;
+			this.shroud = shroud;
 
 			// Consider all cells inside the map area (ignoring the current map bounds)
 			Footprint = footprint
@@ -79,6 +79,7 @@ namespace OpenRA.Traits
 		void UpdateVisibility()
 		{
 			var wasVisible = Visible;
+			var isVisibleTest = shroud.IsVisibleTest;
 
 			// We are doing the following LINQ manually for performance since this is a hot path.
 			// Visible = !Footprint.Any(isVisibleTest);

OpenRA.Game/Traits/World/Shroud.cs

@@ -325,6 +325,11 @@ namespace OpenRA.Traits
 			return explored[uv] && (generatedShroudCount[uv] == 0 || visibleCount[uv] > 0);
 		}
 
+		/// <summary>
+		/// Returns a fast exploration lookup that skips the usual validation.
+		/// The return value should not be cached across ticks, and should not
+		/// be called with cells outside the map bounds.
+		/// </summary>
 		public Func<MPos, bool> IsExploredTest
 		{
 			get
@@ -371,6 +376,11 @@ namespace OpenRA.Traits
 			return visibleCount[uv] > 0;
 		}
 
+		/// <summary>
+		/// Returns a fast visibility lookup that skips the usual validation.
+		/// The return value should not be cached across ticks, and should not
+		/// be called with cells outside the map bounds.
+		/// </summary>
 		public Func<MPos, bool> IsVisibleTest
 		{
 			get