make GiveMcvCrateAction less stupid, if the GiveUnitCrateAction says it can't do it.

OpenRA.Mods.RA/Crates/GiveMcvCrateAction.cs

@@ -26,6 +26,9 @@ namespace OpenRA.Mods.RA.Crates
 
 		public override int GetSelectionShares(Actor collector)
 		{
+			if (base.GetSelectionShares(collector) == 0)
+				return 0;	// there's some other really good reason why we shouldn't give this.
+
 			var hasBase = self.World.Queries.OwnedBy[collector.Owner].WithTrait<BaseBuilding>().Any();
 			return hasBase ? info.SelectionShares : (info as GiveMcvCrateActionInfo).NoBaseSelectionShares;
 		}