Missing check in CDIManagedBeanHandlerImpl causes high amounts of "@SessionScoped does not exist within current thread" exceptions

Since upgrading from 2.3.4 to 2.3.8 we noticed a huge amount of @SessionScoped does not exist within current thread exceptions in our logs.

As tandraschko pointed out on the mailing list this could be a side effect of MYFACES-4353.

Will create some PRs for 2.2, 2.3, 3.0 and 2.3-next shortly.