Handle errors getting state in Unix (dotnet/corefx#27239)

Handle errors getting state in Unix (dotnet/corefx#27239)

* Handle errors getting state in Unix

Throwing errors while examining extended state while enumerating isn't consistent with Windows behavior. Windows never throws past getting directory entry data as all state is already available.

Ensure entry attribute state is consistent with initial construction.

* Win 7 CI machines are also setting NotContentIndexed.

Commit migrated from https://github.com/dotnet/corefx/commit/597f44c5056badfb47f45731480454d698849800