Bug 15844 [Exception Handling] SelectionChange events and NPE
Build 20020508 Due to new global actions there are now more objects listening to selection changes send out by a JFace viewer. We now had the case that one of the listener generated a NPE. As a result all listeners registered after that one didn't receive the selection change event. StructuredViewers should be more fault tolorant to exceptions when informing listeners.
bundles/org.eclipse.jface/src/org/eclipse/jface/viewers/CheckboxTreeViewer.java
/**
	 * List of check state listeners (element type: <code>ICheckStateListener</code>).
	 */
	private ListenerList checkStateListeners = new ListenerList(3);
	/**
	 * Last item clicked on, or <code>null</code> if none.
	 */
	private TreeItem lastClickedItem = null;	
/**
 * Creates a tree viewer on a newly-created tree control under the given parent.
 * The tree control is created using the SWT style bits: <code>CHECK</code> and <code>BORDER</code>.
 * The viewer has no input, no content provider, a default label provider,