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/AbstractTreeViewer.java
*/
private Item rightMostVisibleDescendent(Item item) {
	Item[] children = getItems(item);
	if (getExpanded(item) && children != null && children.length > 0) {
		return rightMostVisibleDescendent(children[children.length-1]);
	} else {
		return item;
	}
}
/* (non-Javadoc)
 * Method declared on Viewer.
 */
public Item scrollDown(int x, int y) {
	Item current = getItem(x, y);
	if (current != null) {
		Item next = getNextItem(current, true);
		showItem(next == null ? current : next);
		return next;
	}
	return null;
}
/* (non-Javadoc)
 * Method declared on Viewer.
 */
public Item scrollUp(int x, int y) {
	Item current = getItem(x, y);
	if (current != null) {
		Item previous = getPreviousItem(current);
		showItem(previous == null ? current : previous);
		return previous;