fix: avoid deleting objects two times

This patch fix crash that happens when quitting the app.
https://git.ring.cx/savoirfairelinux/ring-client-macosx/issues/156

Change-Id: Icec9562e80ce09feded17399327c535a98e0ef34

src/AppDelegate.mm

@@ -334,7 +334,7 @@ static void ReachabilityCallback(SCNetworkReachabilityRef __unused target, SCNet
 
 - (void)handleQuitEvent:(NSAppleEventDescriptor*)event withReplyEvent:(NSAppleEventDescriptor*)replyEvent
 {
-    [self cleanExit];
+    [[NSApplication sharedApplication] terminate:self];
 }
 
 -(void)applicationWillTerminate:(NSNotification *)notification