Description of problem:
ArrayIndexOutOfBoundsException occurs when a queue-length is 0 in the thread pool executor.

Exception in thread "testTP-threads - 1" java.lang.ArrayIndexOutOfBoundsException: 0
	at org.jboss.threads.ArrayQueue.poll(ArrayQueue.java:118)
	at org.jboss.threads.QueueExecutor.takeTask(QueueExecutor.java:713)
	at org.jboss.threads.QueueExecutor.access$400(QueueExecutor.java:45)
	at org.jboss.threads.QueueExecutor$Worker.run(QueueExecutor.java:842)
	at java.lang.Thread.run(Thread.java:745)
	at org.jboss.threads.JBossThread.run(JBossThread.java:122)


Version-Release number of selected component (if applicable):
EAP 6.4.1

Steps to Reproduce:
1. Set the thread pool executor.
~~~
[standalone@localhost:9999 /] /subsystem=threads/bounded-queue-thread-pool=testTP:add(max-threads=10, queue-length=0)
{"outcome" => "success"}
[standalone@localhost:9999 /] /subsystem=web/connector=http:write-attribute(name=executor,value=testTP)
{
    "outcome" => "success",
    "response-headers" => {
        "operation-requires-reload" => true,
        "process-state" => "reload-required"
    }
}
[standalone@localhost:9999 /] reload
~~~

2. Execute "http://localhost:8080/" in your browser.

3. You can confirm the ArrayIndexOutOfBoundsException in your server log.