Merge pull request #4832 from ScottNZ/guard-og-fix

Fix Guard OG crash #4821

CHANGELOG

@@ -22,6 +22,7 @@ NEW:
 		Removed the ability of commandos to plant C4 on walls.
 		Order lines are now shown on unit selection.
 		Fixed chat synchronization in replays.
+		Fixed the game sometimes crashing when deploying and activating the guard cursor at the same time.
 	Dune 2000:
 		Added the Atreides grenadier from the 1.06 patch.
 		Added randomized tiles for Sand and Rock terrain.

OpenRA.Mods.RA/Guard.cs

@@ -84,6 +84,9 @@ namespace OpenRA.Mods.RA
 
 		public string GetCursor(World world, CPos xy, MouseInput mi)
 		{
+			if (!subjects.Any())
+				return null;
+
 			var multiple = subjects.Count() > 1;
 			var canGuard = FriendlyGuardableUnits(world, mi)
 				.Any(a => multiple || a != subjects.First());