fix(iOS, Tabs): fix diverging behavior of JS updates requesting moreNavigationController on various Apple platforms (#3813)

Fix-up `moreNavigationController` handling on platforms where it is not
available
I've introduced a bug in
[#3785](https://github.com/software-mansion/react-native-screens/pull/3785/changes#diff-24866ece8ac586353673ecc0296de6ac8be5c1df28f12039774c9580bd5750d3).
If the code runs on a platform where `moreNavigationController` is not
available,
the whole code for handling update requesting the
`moreNavigationController` won't execute - the update will not be
rejected
as on other platforms, but rather the asserts will crash (in debug).

Author: kkafar

ios/tabs/host/RNSTabBarController.mm

@@ -349,20 +349,19 @@ - (void)updateSelectedViewController
   UIViewController *nextSelectedViewController = nil;
   BOOL isNextMoreNavigationController = NO;
 
-#if RNS_MORE_NAVIGATION_CONTROLLER_AVAILABLE
   if ([self isMoreNavigationControllerRequestedByOperation:_pendingOperation]) {
     if (![self isMoreNavigationControllerPresentInTabBar]) {
       // If the controller is not visible atm. we'll crash the app.
       // TODO: Emit rejection event
       _pendingOperation = nil;
       return;
     }
-    nextSelectedViewController = self.moreNavigationController;
+    nextSelectedViewController = [self resolveMoreNavigationController];
+    RCTAssert(nextSelectedViewController != nil, @"[RNScreens] Expected non-nil moreNavigationController");
     isNextMoreNavigationController = YES;
   } else {
     nextSelectedViewController = [self findChildViewControllerForKey:nextSelectedViewControllerKey];
   }
-#endif // RNS_MORE_NAVIGATION_CONTROLLER_AVAILABLE
 
   RCTAssert(
       nextSelectedViewController != nil,
@@ -605,6 +604,23 @@ - (void)setupMoreNavigationControllerDelegateIfNeeded
 #endif // RNS_MORE_NAVIGATION_CONTROLLER_AVAILABLE
 }
 
+/**
+ * This method allows getting the `moreNavigationController` instance under a couple of conditions.
+ *
+ * First, it verifies whether we are on an appropriate platform, where the `moreNavigationController`
+ * is available.
+ * Second, it verifies whether the `moreNavigationController` can even be in the interface right now.
+ */
+- (nullable UINavigationController *)resolveMoreNavigationController
+{
+#if RNS_MORE_NAVIGATION_CONTROLLER_AVAILABLE
+  if ([self canHaveMoreNavigationController]) {
+    return self.moreNavigationController;
+  }
+#endif // RNS_MORE_NAVIGATION_CONTROLLER_AVAILABLE
+  return nil;
+}
+
 #if !RCT_NEW_ARCH_ENABLED
 
 #pragma mark - LEGACY Paper scheduling methods