Fix vmware layer so that files without a vmss or vmsn are still constructed with the warning is shown

[eve-mem]

Hello 👋

User Super_Snorlax on slack raised an issue where a vmware sample failed to work with a .vmem extension but did with a .raw extension.

They've yet to report having tested this change but I suspect it will fix the issue.

I believe this return None incorrectly stops some samples for working. The warning says may be required but the return None is meaning it will never be stacked.

🦊

[eve-mem]

Actually the discussion on the where the warning was added #1016

It seems like the return None is okay. I'm changing this to draft until I hear from Super_Snorlax if this fixes the problem. (Or if I get my hands on a a flat vmware image type to test against)

[eve-mem]

Super_Snorlax provided a sample and this did not help in the slightest. I'd got completely the wrong end of the stick.