Bug 39027 [working sets] Edit active working set prevents removal of closed projects.
When editing the "active working set" closed projects cannot be removed from the working set, the project has to be opened so it can be removed. This is a minor usability issue.
org.eclipse.jdt.ui/ui/org/eclipse/jdt/internal/ui/workingsets/JavaWorkingSetPage.java
String newText= fWorkingSetName.getText();
		if (newText.equals(newText.trim()) == false)
			errorMessage = WorkingSetMessages.getString("JavaWorkingSetPage.warning.nameWhitespace"); 
		if (newText.equals("")) { 
			if (fFirstCheck) {
				setPageComplete(false);
				fFirstCheck= false;
				return;
			}
			else				
				errorMessage= WorkingSetMessages.getString("JavaWorkingSetPage.warning.nameMustNotBeEmpty"); 
		}
		fFirstCheck= false;
		if (errorMessage == null && (fWorkingSet == null || newText.equals(fWorkingSet.getName()) == false)) {
			IWorkingSet[] workingSets= PlatformUI.getWorkbench().getWorkingSetManager().getWorkingSets();
			for (int i= 0; i < workingSets.length; i++) {
				if (newText.equals(workingSets[i].getName())) {
					errorMessage= WorkingSetMessages.getString("JavaWorkingSetPage.warning.workingSetExists"); 
				}
			}
		}
		if (errorMessage == null && !hasCheckedElement())
			errorMessage= WorkingSetMessages.getString("JavaWorkingSetPage.warning.resourceMustBeChecked"); 
		setErrorMessage(errorMessage);
		setPageComplete(errorMessage == null);
	}
	
	private boolean hasCheckedElement() {
		TreeItem[] items= fTree.getTree().getItems();
		for (int i= 0; i < items.length; i++) {