Fix AppDomain.SetPrincipalPolicy bug for new threads

[MarcoRossignoli]

Fixes #31717

Old code did

return CurrentThread._principal ?? (CurrentThread._principal = AppDomain.CurrentDomain.GetThreadPrincipal());

I missed to bring principal null check 😡

cc: @jkotas @stephentoub

PS. Debug cross repo is great(lib->coreclr), but it's a bit slow due to debug build of EE, is there a way to build EE in release and only managed part(System.Private.CoreLib) in debug?

[MarcoRossignoli]

Got this error from CI https://helix.dot.net/api/2019-06-17/jobs/c7ca5c04-d00f-417f-9b34-3e48d889129d/workitems/System.Threading.Tasks.Tests/console but seem unrelated to my update.

[MarcoRossignoli]

/azp list

[azure-pipelines]

Commenter does not have sufficient privileges for PR 32104 in repo dotnet/runtime

[jkotas]

The CI error is known problem. All PRs are hitting it.

[jkotas]

is there a way to build EE in release and only managed part

https://github.com/dotnet/runtime/blob/master/docs/workflow/building/libraries/README.md

[MarcoRossignoli]

https://github.com/dotnet/runtime/blob/master/docs/workflow/building/libraries/README.md

Not sure there is what I would...for clr cannot build EE in release and c# in debug I can only specify one -c, btw no probs

[jkotas]

Thank you!

[jkotas]

The test failures are known issue #32126