gpu/d3d12: Acknowledge that we've bound vertex buffers (#13088)

src/gpu/d3d12/SDL_gpu_d3d12.c

@@ -4961,6 +4961,8 @@ static void D3D12_INTERNAL_BindGraphicsResources(
             0,
             commandBuffer->vertexBufferCount,
             vertexBufferViews);
+
+        commandBuffer->needVertexBufferBind = false;
     }
 
     if (commandBuffer->needVertexSamplerBind) {