When a render method has nothing to render, eagerly return.

By eagerly returning an empty enumerable in these cases, this avoids allocating an enumerable for the whole render method if nothing will be drawn.

OpenRA.Mods.Common/Traits/HitShape.cs

@@ -90,8 +90,13 @@ namespace OpenRA.Mods.Common.Traits
 		IEnumerable<WPos> ITargetablePositions.TargetablePositions(Actor self)
 		{
 			if (IsTraitDisabled)
-				yield break;
+				return Enumerable.Empty<WPos>();
 
+			return TargetablePositions(self);
+		}
+
+		IEnumerable<WPos> TargetablePositions(Actor self)
+		{
 			if (Info.UseTargetableCellsOffsets && targetableCells != null)
 				foreach (var c in targetableCells.TargetableCells())
 					yield return self.World.Map.CenterOfCell(c.Cell);