Dispatch safariViewController on main queue

The safariViewController dispatch was occuring on another thread.
This sometimes caused app crashes when the view was presented,
in particular if the keyboard had been presented via a TextInput or
other component. The resulting crash complained about
_cachedSystemAnimationFence and the main thread. This has been with
other React Native apps that load a viewController.

Dispatching to present the viewController on the main thread fixes this
issue.

Author: stonehippo

ios/OAuthManager/OAuthManager.m

@@ -91,7 +91,9 @@ + (BOOL)setupOAuthHandler:(UIApplication *)application
             dispatch_async(dispatch_get_main_queue(), ^{
                 safariViewController = [[SFSafariViewController alloc] initWithURL:URL];
                 UIViewController *viewController = application.keyWindow.rootViewController;
-                [viewController presentViewController:safariViewController animated:YES completion: nil];
+                dispatch_async(dispatch_get_main_queue(), ^{
+                    [viewController presentViewController:safariViewController animated:YES completion: nil];
+                });
             });
         } else {
             [application openURL:URL];