Fix NoSuchElementException in Hystrix.endCurrentThreadExecutingCommand

If a semaphore isolated HystrixCommand gets a response from a request cache this exception will be thrown:

Caused by: java.util.NoSuchElementException
        at java.util.LinkedList.removeFirst(LinkedList.java:268)
        at java.util.LinkedList.pop(LinkedList.java:799)
        at com.netflix.hystrix.Hystrix.endCurrentThreadExecutingCommand(Hystrix.java:88)
        at com.netflix.hystrix.HystrixCommand.queueInSemaphore(HystrixCommand.java:647)
        at com.netflix.hystrix.HystrixCommand.queue(HystrixCommand.java:551)
        at com.netflix.platform.dependencycommand.NFDependencyCommand.queue(NFDependencyCommand.java:346)
Merge pull request #133 from benjchristensen/fix-error-handling-endCurrentThreadExecutingCommand

Fix NoSuchElementException in Hystrix.endCurrentThreadExecutingCommand