Introduce FirstOrDefault extensions method for Array.Find and List.Find.

This allows the LINQ spelling to be used, but benefits from the performance improvement of the specific methods for these classes that provide the same result.

OpenRA.Mods.Common/Traits/Player/GameSaveViewportManager.cs

@@ -9,7 +9,6 @@
  */
 #endregion
 
-using System;
 using System.Collections.Generic;
 using OpenRA.Graphics;
 using OpenRA.Traits;
@@ -34,7 +33,7 @@ namespace OpenRA.Mods.Common.Traits
 			// TODO: This won't make sense for MP saves
 			var localPlayer = worldRenderer.World.LocalPlayer;
 			if ((localPlayer != null && localPlayer.PlayerActor != self) ||
-				(localPlayer == null && self.Owner != Array.Find(self.World.Players, p => p.IsBot)))
+				(localPlayer == null && self.Owner != self.World.Players.FirstOrDefault(p => p.IsBot)))
 				return null;
 
 			var nodes = new List<MiniYamlNode>()