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/SemanticHighlightingReconciler.java
return;
		
		Shell shell= site.getShell();
		if (shell == null || shell.isDisposed())
			return;
		
		Display display= shell.getDisplay();
		if (display == null || display.isDisposed())
			return;
		
		display.asyncExec(runnable);
	}
	
	/**
	 * Stop reconciling positions.
	 */
	private void stopReconcilingPositions() {
		fRemovedPositions.clear();
		fNOfRemovedPositions= 0;
		fAddedPositions.clear();
	}
	/**
	 * Install this reconciler on the given editor, presenter and highlightings.
	 * @param editor the editor
	 * @param sourceViewer the source viewer
	 * @param presenter the semantic highlighting presenter
	 * @param semanticHighlightings the semantic highlightings
	 * @param highlightings the highlightings
	 */
	public void install(JavaEditor editor, ISourceViewer sourceViewer, SemanticHighlightingPresenter presenter, SemanticHighlighting[] semanticHighlightings, Highlighting[] highlightings) {