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
break;
					--offset;
				}
	
				int start= offset;
	
				offset= anchor;
				int length= document.getLength();
	
				while (offset < length) {
					c= document.getChar(offset);
					if (!Character.isJavaIdentifierPart(c))
						break;
					++offset;
				}
				
				int end= offset;
				
				if (start == end)
					return new Region(start, 0);
				else
					return new Region(start + 1, end - start - 1);
				
			} catch (BadLocationException x) {
				return null;
			}
		}
		IRegion getCurrentTextRegion(ISourceViewer viewer) {
			int offset= getCurrentTextOffset(viewer);				
			if (offset == -1)