Fixed unnecessary zero-length array allocations

Changed all currently present zero-length array allocations in the codebase to use `Array.Empty` instead.

OpenRA.Mods.Cnc/SpriteLoaders/TmpRALoader.cs

@@ -9,6 +9,7 @@
  */
 #endregion
 
+using System;
 using System.IO;
 using OpenRA.Graphics;
 using OpenRA.Primitives;
@@ -32,7 +33,7 @@ namespace OpenRA.Mods.Cnc.SpriteLoaders
 				Data = data;
 
 				if (data == null)
-					Data = new byte[0];
+					Data = Array.Empty<byte>();
 				else
 					Size = size;
 			}