Fix #1230: crash when no hpad owned by player

OpenRA.Mods.RA/Air/HeliReturn.cs

@@ -37,10 +37,12 @@ namespace OpenRA.Mods.RA.Air
 				var nearestHpad = self.World.ActorsWithTrait<Reservable>()
 									.Where(a => a.Actor.Owner == self.Owner && rearmBuildings.Contains(a.Actor.Info.Name))
 									.Select(a => a.Actor)
-									.ClosestTo(self.CenterLocation);
-
-				self.CancelActivity();
-				return Util.SequenceActivities(new HeliFly(Util.CenterOfCell(nearestHpad.Location)));
+									.ClosestTo(self.CenterLocation);
+
+				if (nearestHpad == null)
+					return Util.SequenceActivities(new Turn(initialFacing), new HeliLand(true), NextActivity);
+				else
+					return Util.SequenceActivities(new HeliFly(Util.CenterOfCell(nearestHpad.Location)));
 			}
 
 			var res = dest.TraitOrDefault<Reservable>();