Examples: DirectX12: Fixed shutdown issue. (#301)

examples/directx12_example/main.cpp

@@ -396,7 +396,7 @@ int main(int, char**)
         g_pd3dCommandList->ResourceBarrier(1, &barrier);
         g_pd3dCommandList->Close();
 
-        g_pd3dCommandQueue->ExecuteCommandLists(1, (ID3D12CommandList* const*) &g_pd3dCommandList);
+        g_pd3dCommandQueue->ExecuteCommandLists(1, (ID3D12CommandList* const*)&g_pd3dCommandList);
 
         g_pSwapChain->Present(1, 0); // Present with vsync
         //g_pSwapChain->Present(0, 0); // Present without vsync
@@ -407,9 +407,9 @@ int main(int, char**)
         frameCtxt->FenceValue = fenceValue;
     }
 
+    WaitForLastSubmittedFrame();
     ImGui_ImplDX12_Shutdown();
     ImGui::DestroyContext();
-
     CleanupDeviceD3D();
     UnregisterClass(_T("ImGui Example"), wc.hInstance);