Steps to reproduce:

1. Open attached project "954098.zip"
2. Make sure selected Graphics API is Direct3D12
3. Open "main" scene
4. Select "Main Camera" in the Hierarchy
5. Make sure 'Color AA' and 'Depth AA' are set to 'X1' in RenderBuffer script component
6. Enter play mode
7. Set 'Color AA' to 'X2' in RenderBuffer script component
8. Set 'Depth AA' to 'X2' in RenderBuffer script component
*by this time Editor freezes*
9. Try to change 'Color AA' or 'Depth AA' or exit play mode

Actual result: editor crashes in D3D12SwapChain::CreateHWND (log attached)

Reproducible with: 2017.3.0f1, 2018.1.0a6

Note: if you change 'Color AA' and 'Depth AA' before entering play mode, the editor will freeze but won't crash when entering play mode

Not reproducible with DirectX11, OpenGL4.5