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
stopReconcilingPositions();
		
		fJobPresenter= null;
		fJobSemanticHighlightings= null;
		fJobHighlightings= null;
	}
	
	/**
	 * @param node Root node
	 * @return Array of subtrees that may be affected by past document changes
	 */
	private ASTNode[] getAffectedSubtrees(ASTNode node) {
		
		return new ASTNode[] { node };
	}
	/**
	 * Start reconciling positions.
	 */
	private void startReconcilingPositions() {
		fJobPresenter.addAllPositions(fRemovedPositions);
		fNOfRemovedPositions= fRemovedPositions.size();
	}
	
	/**
	 * Reconcile positions based on the AST subtrees
	 * 
	 * @param subtrees the AST subtrees
	 */
	private void reconcilePositions(ASTNode[] subtrees) {