Bug 43488 [typing] BadPositionCategoryException in LinkedPositionManager
org.eclipse.jdt.ui/ui/org/eclipse/jdt/internal/ui/text/link/contentassist/ContentAssistant2.java
* @return <code>true</code> if the listener could be added
	 */
	boolean addContentAssistListener(IContentAssistListener2 listener, int type) {
		
		if (acquireWidgetToken(type)) {
			
			fListeners[type]= listener;
			
			if (getNumberOfListeners() == 1) {
				fCloser= new Closer();
				fCloser.install();
				fViewer.setEventConsumer(fInternalListener);
				installKeyListener();
			}
			return true;
		}
		
		return false;
	}
	
	/**
	 * Installs a key listener on the text viewer's widget.
	 */
	private void installKeyListener() {
		if (!fKeyListenerHooked) {
			StyledText text= fViewer.getTextWidget();
			if (Helper2.okToUse(text)) {
				
				if (fViewer instanceof ITextViewerExtension) {
					ITextViewerExtension e= (ITextViewerExtension) fViewer;