Merge pull request #3362 from artem-zinnatullin/fix-synchronization-o…

…n-non-final-field-in-BufferUntilSubscriber

Fix synchronization on non-final field in BufferUntilSubscriber

src/main/java/rx/internal/operators/BufferUntilSubscriber.java

@@ -70,7 +70,7 @@ boolean casObserverRef(Observer<? super T>  expected, Observer<? super T>  next)
             return OBSERVER_UPDATER.compareAndSet(this, expected, next);
         }
 
-        Object guard = new Object();
+        final Object guard = new Object();
         /* protected by guard */
         boolean emitting = false;