Bug 75711 AstProvider should not create AST if requested by SelectionListenerWithASTManager
3.1 M2 If SelectionListenerWithASTManager waits for an AST and the editor closes we should not create an AST for that one but return null instead.
org.eclipse.jdt.ui/ui/org/eclipse/jdt/internal/ui/javaeditor/JavaEditor.java
if (event.getProperty().equals(JavaEditor.LINK_COLOR)) {
				ISourceViewer viewer= getSourceViewer();
				if (viewer != null)	
					updateColor(viewer);
			} else if (event.getProperty().equals(BROWSER_LIKE_LINKS_KEY_MODIFIER)) {
				updateKeyModifierMask();
			}
		}
		private void updateColor(ISourceViewer viewer) {
			if (fColor != null)
				fColor.dispose();
	
			StyledText text= viewer.getTextWidget();
			if (text == null || text.isDisposed())
				return;
			Display display= text.getDisplay();
			fColor= createColor(getPreferenceStore(), JavaEditor.LINK_COLOR, display);
		}
		/**
		 * Creates a color from the information stored in the given preference store.
		 * 
		 * @param store the preference store
		 * @param key the key
		 * @param display the display
		 * @return the color or <code>null</code> if there is no such information available 
		 */
		private Color createColor(IPreferenceStore store, String key, Display display) {
		
			RGB rgb= null;