Bug 50022 [DND] NPE in DelegatingDragAdapter
DelegatingDragAdapater defines a list "activeListeners" but initializes it only in DragStart. However, the list is referenced in removeDragSourceListener without a null check, thus causing a null pointer exception if no dragStart ever occured.
bundles/org.eclipse.jface/src/org/eclipse/jface/util/DelegatingDragAdapter.java
private TransferDragSourceListener currentListener;
	/**
	 * Adds the given <code>TransferDragSourceListener</code>.
	 * 
	 * @param listener the new listener
	 */
	public void addDragSourceListener(TransferDragSourceListener listener) {
		listeners.add(listener);
	}
	/**
	 * The drop has successfully completed. This event is forwarded to the current 
	 * drag listener.
	 * Doesn't update the current listener, since the current listener  is already the one
	 * that completed the drag operation.
	 * 
	 * @param event the drag source event
	 * @see DragSourceListener#dragFinished(DragSourceEvent)
	 */
	public void dragFinished(final DragSourceEvent event) {
		Platform.run(new SafeRunnable() {
			public void run() throws Exception {					
				if (currentListener != null) {
					
					currentListener.dragFinished(event);
				}
				else {
					
					 
					Iterator iterator = activeListeners.iterator();
					while (iterator.hasNext())