message: Add check for open folder.
diff: @@ -787,11 +787,12 @@ export class CMakeTools implements vscode.Disposable, api.CMakeToolsAPI {
  * Implementation of `cmake.quickStart`
  */
  public async quickStart(): Promise<Number> {
  - let sourceDir = vscode.workspace.rootPath!;
  - if( vscode.workspace.workspaceFolders !== null) {
  - sourceDir = vscode.workspace.workspaceFolders![0].uri.fsPath;
  + if (vscode.workspace.workspaceFolders === undefined) {
  + vscode.window.showErrorMessage('No folder is open.');
  + return -2;
  }
  + const sourceDir = vscode.workspace.workspaceFolders![0].uri.fsPath;
  const mainListFile = path.join(sourceDir, 'CMakeLists.txt');
  if (await fs.exists(mainListFile)) {
  