CMakeOpenProjectWizard: The user needs to always select a kit

So check that in isComplete() and prevent a crash.

Task-number: QTCREATORBUG-8717
Change-Id: Ib485941534a4f0f3aa4e791fdb655eb9061ba9fa
Reviewed-by: Tobias Hunger <tobias.hunger@digia.com>

src/plugins/cmakeprojectmanager/cmakeopenprojectwizard.h

@@ -189,7 +189,6 @@ private:
     QLabel *m_descriptionLabel;
     QLabel *m_exitCodeLabel;
     bool m_haveCbpFile;
-    bool m_optionalCMake;
     Mode m_mode;
     QString m_buildDirectory;
 };