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/ASTProvider.java
final IJavaElement activeElement= fReconcilingJavaElement;
				
				
				synchronized (fWaitLock) {
					if (DEBUG)
						System.out.println(DEBUG_PREFIX + "waiting for AST for: " + je.getElementName()); 
					
					fWaitLock.wait();
				}
				
				
				synchronized (this) {
					if (activeElement == fActiveJavaElement) {
						if (DEBUG)
							System.out.println(DEBUG_PREFIX + "...got AST for: " + je.getElementName()); 
						
						return fAST;
					}
				}
				return getAST(je, wait, progressMonitor);
			} catch (InterruptedException e) {
			}
		} else if (!wait)
			return null;
		
		CompilationUnit ast= createAST(je, progressMonitor);
		if (progressMonitor != null && progressMonitor.isCanceled())
			return null;
		
		if (DEBUG)