- fixed crash in AutoUseStrifeHealth

The loop never checked if the item was still valid and would continue to try to use it, even after it was removed from the inventory and destroyed.
As native code this just failed silently, but with the VM it needs to be explicitly checked.

wadsrc/static/zscript/shared/player_inventory.txt

@@ -309,7 +309,8 @@ extend class PlayerPawn
 
 				while (player.health < 50)
 				{
-					if (!UseInventory (Items[index]))
+					let item = Items[index];
+					if (item == null || !UseInventory (item))
 						break;
 				}
 				if (player.health >= 50) return;