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.Game/Exts.cs

@@ -135,6 +135,16 @@ namespace OpenRA
 			return Array.IndexOf(array, value);
 		}
 
+		public static T FirstOrDefault<T>(this T[] array, Predicate<T> match)
+		{
+			return Array.Find(array, match);
+		}
+
+		public static T FirstOrDefault<T>(this List<T> list, Predicate<T> match)
+		{
+			return list.Find(match);
+		}
+
 		public static T Random<T>(this IEnumerable<T> ts, MersenneTwister r)
 		{
 			return Random(ts, r, true);