Landscape dominant layer lost when changing collision mip level

Hi Luis, Thanks for your report. This was fixed for Unreal Engine 4.8, and the source code change can be found here:

https://github.com/EpicGames/UnrealEngine/commit/d52313fd6ad4dd9a88093119506127c3b71a6c72

This fix should also be in any of the 4.8 preview versions if you want to try.

Thanks