Create command buffers when rented rather than in advance (#31)

* Make it less likely to freeze, but the creation of the command buffer should probably be moved

* Create command buffers as they're rented rather than in advance

src/Ryujinx.Graphics.Metal/BackgroundResources.cs

@@ -26,7 +26,7 @@ namespace Ryujinx.Graphics.Metal
             if (_pool == null)
             {
                 MTLCommandQueue queue = _renderer.BackgroundQueue;
-                _pool = new CommandBufferPool(queue);
+                _pool = new CommandBufferPool(queue, true);
                 _pool.Initialize(null); // TODO: Proper encoder factory for background render/compute
             }