[Fix] Bugzilla #18182 - ConcurrentQueue<T>.TryPeek() is not thread safe
- in the previous version the IsEmpty could be false, but by time we get
  to head.Next.Value we get an exception since Value is now null
- passes existing test cases, although these are not definitive since
  they don't show threading issue
- would need to adapt System.Threading.Tasks.ParallelTestHelper to allow
  TryPeek() to be called during Enqueue/Dequeue operations to truly
  test this change out
[Fix] Bugzilla #18182 - ConcurrentQueue<T>.TryPeek() is not thread safe
- removed IsEmpty test from TryPeek() since not needed now
Merge pull request #932 from exony-craigminihan/bugzilla#18182

[Fix] Bugzilla #18182 - ConcurrentQueue<T>.TryPeek() is not thread safe