Update AbstractNodeQueue.java

Avoid spinning on head when a peek/poll observes a null next but the queue is not empty.
Update AbstractNodeQueue.java

language language....
=con #15600 Fix config in PeekMailboxSpec
Merge pull request #15601 from LeonardMeyer/LMeyer-specfix-#15600

=con #15600 Fix config in PeekMailboxSpec
Add abbrev for project changes to CONTRIBUTING.md

As noticed during https://github.com/akka/akka/pull/15617, we didn't hint people to use `=pro` when changing things in the project / build.
=pro #15616 UTF-8 charset and exception with offending file (for Validation)
Merge pull request #15623 from ktoso/port-15616-master-ktoso

=pro #15616 UTF-8 charset and exception with offending file (for Validation)
=doc #15565 improved wording in cluster-usage docs
Merge pull request #15624 from ktoso/docs-cluster-joining-ktoso

=doc #15565 improved wording in cluster-usage docs
=con #15613 Rename one of the DistributedPubSubMediatorSpec classes
=doc Fix typo in scala remoting.rst
Merge pull request #15630 from savulchik/patch-1

Fix typo in scala remoting.rst
+con #13737 Interceptors chain for Actors' bahavior.

* Add new pattern to akka-contrib.
* Mixin ReceivePipeline trait into Actors that have to be intercepted.
Merge pull request #15629 from akka/wip-15613-rename-DistributedPubSubMediatorSpec-patriknw

=con #15613 Rename one of the DistributedPubSubMediatorSpec classes
=tes #15167 Harden TestTimeSpec
Merge pull request #1869 from ktonga/wip-3737-interceptors-chain-for-receive-ktonga

#3737 Interceptors chain for receive
+act - #15501 - Adding support for a Non-blocking, bounded, MPMC mailbox called 'NonBlockingBoundedMailbox'
Fix isEmpty() and count()

isEmpty() need not rely on peek(which is intended for consumer use) and instead compare head to tail.
count() should stop counting at max int to avoid wrap.
Fixe documentation to state consumer only access is allowed to poll/peek/peekNode/pollNode
Doc stars err