Fix crashes related to transports

Fixes two specific causes of transport related crashes, one prevents
infantry from continuing to take damage by Tiberium if loaded into the
transport over Tiberium, and one fixes the edge case where an infantry
dies in the same tick cycle as it was loaded into the transport.

OpenRA.Mods.Cnc/PoisonedByTiberium.cs

@@ -32,6 +32,9 @@ namespace OpenRA.Mods.Cnc
 		{
 			if (--poisonTicks > 0) return;
 
+			// Prevents harming infantry in cargo.
+			if (!self.IsInWorld) return;
+
 			var rl = self.World.WorldActor.Trait<ResourceLayer>();
 			var r = rl.GetResource(self.Location);
 			if (r == null) return;

OpenRA.Mods.RA/Activities/EnterTransport.cs

@@ -41,8 +41,14 @@ namespace OpenRA.Mods.RA.Activities
 			if (!cells.Contains(self.Location))
 				return NextActivity;
 
+			self.World.AddFrameEndTask(w => 
+			{
+				if(self.IsDead() || transport.IsDead() || !cargo.CanLoad(transport, self))
+					return;
+
 				cargo.Load(transport, self);
-			self.World.AddFrameEndTask(w => w.Remove(self));
+				w.Remove(self);
+			});
 
 			return this;
 		}