Don't give a levelup crate if the unit can't gain experience

OpenRA.Mods.RA/Crates/LevelUpCrateAction.cs

@@ -19,7 +19,13 @@ namespace OpenRA.Mods.RA
 	{
 		public LevelUpCrateAction(Actor self, LevelUpCrateActionInfo info)
 			: base(self,info) {}
-
+		
+		public override int GetSelectionShares(Actor collector)
+		{
+			var ge = collector.TraitOrDefault<GainsExperience>();
+			return ge != null && ge.Level < ge.MaxLevel ? info.SelectionShares : 0;
+		}
+		
 		public override void Activate(Actor collector)
 		{
 			collector.World.AddFrameEndTask(w =>

OpenRA.Mods.RA/GainsExperience.cs

@@ -56,6 +56,7 @@ namespace OpenRA.Mods.RA
 		int Experience = 0;
 		[Sync]
 		public int Level { get; private set; }
+		public int MaxLevel { get { return Levels.Length; } }
 
 		public void GiveOneLevel()
 		{