Add property requirements to safe traits

OpenRA.Mods.Common/Traits/GlobalUpgradable.cs

@@ -16,10 +16,11 @@ namespace OpenRA.Mods.Common.Traits
 	[Desc("Grants upgrades to the actor this is attached to when prerequisites are available.")]
 	public class GlobalUpgradableInfo : ITraitInfo, Requires<UpgradeManagerInfo>
 	{
-		[UpgradeGrantedReference]
+		[UpgradeGrantedReference, FieldLoader.Require]
 		[Desc("List of upgrades to apply.")]
 		public readonly string[] Upgrades = { };
 
+		[FieldLoader.Require]
 		[Desc("List of required prerequisites.")]
 		public readonly string[] Prerequisites = { };