Addresses flicker bug in scrumptious

Summary:
Moves the delayed call back one frame in the stack, in order to avoid
its being active in the startup case

Test Plan: Ran the app

Reviewers: clang, chrisp

Reviewed By: clang

CC: msdkexp@

Differential Revision: https://phabricator.fb.com/D583546

Task ID: 1731992

samples/Scrumptious/scrumptious/SCAppDelegate.m

@@ -52,7 +52,7 @@ - (void)createAndPresentLoginView {
 
 - (void)showLoginView {
     if (self.loginViewController == nil) {
-        [self performSelector:@selector(createAndPresentLoginView) withObject:nil afterDelay:0.5f];
+        [self createAndPresentLoginView];
     } else {
         [self.loginViewController loginFailed];
     }
@@ -88,15 +88,20 @@ - (void)sessionStateChanged:(FBSession *)session
                 // Once the user has logged out, we want them to be looking at the root view.
                 UIViewController *topViewController = [self.navController topViewController];
                 UIViewController *modalViewController = [topViewController modalViewController];
-                while (modalViewController != nil) {
+                if (modalViewController != nil) {
                     [topViewController dismissModalViewControllerAnimated:NO];
-                    modalViewController = [topViewController modalViewController];
                 }
                 [self.navController popToRootViewControllerAnimated:NO];
 
                 [FBSession.activeSession closeAndClearTokenInformation];
 
-                [self showLoginView];
+                // if the token goes invalid we want to switch right back to
+                // the login view, however we do it with a slight delay in order to
+                // account for a race between this and the login view dissappearing
+                // a moment before
+                [self performSelector:@selector(showLoginView)
+                           withObject:nil
+                           afterDelay:0.5f];
             }
             break;
         default: