#5916 fix multiple drop things (#5917)

* #5916 fix multiple drop things

* Update orleans/Adventure/AdventureGrains/PlayerGrain.cs

---------

Co-authored-by: David Pine <[email protected]>

Author: ondrelogin

orleans/Adventure/AdventureGrains/PlayerGrain.cs

@@ -26,8 +26,12 @@ public override Task OnActivateAsync(CancellationToken cancellationToken)
     async Task IPlayerGrain.Die()
     {
         // Drop everything
-        var tasks = _things.Select(Drop).ToList();
-        await Task.WhenAll(tasks);
+        var dropTasks = new List<Task<string?>>();        
+        foreach (var thing in _things.ToArray() /* New collection */)
+        {
+            dropTasks.Add(Drop(thing));
+        }
+        await Task.WhenAll(dropTasks);
 
         // Exit the game
         if (_roomGrain is not null && _myInfo is not null)