xconfig: Abort close if configuration cannot be saved

Give the user an opportunity to fix the error or save the configuration
under a different path.

Reported-by: Hiromu Yakura <hiromu1996@gmail.com>
Signed-off-by: Michal Marek <mmarek@suse.cz>

scripts/kconfig/qconf.h

@@ -311,7 +311,7 @@ public slots:
 	void listFocusChanged(void);
 	void goBack(void);
 	void loadConfig(void);
-	void saveConfig(void);
+	bool saveConfig(void);
 	void saveConfigAs(void);
 	void searchConfig(void);
 	void showSingleView(void);