Add additional checks for calculating header height

ios/RNSScreen.mm

@@ -1058,40 +1058,42 @@ - (BOOL)hasNestedStack
   return NO;
 }
 
-- (CGFloat)getNavigationBarHeightIsModal:(BOOL)isModal
+- (UINavigationController *)getVisibleNavigationControllerIsModal:(BOOL)isModal
 {
   UINavigationController *navctr = self.navigationController;
 
-  // In case where screen is a modal, we want to calculate childViewController's
-  // navigation bar height instead of the navigation controller from RNSScreen.
-  if (isModal && self.assertModalHierarchy) {
-    navctr = self.childViewControllers[0];
+  if (isModal) {
+    // In case where screen is a modal, we want to calculate childViewController's
+    // navigation bar height instead of the navigation controller from RNSScreen.
+    if (self.assertModalHierarchy) {
+      navctr = self.childViewControllers[0];
+    } else {
+      // If the modal does not meet requirements (there's no RNSNavigationController which means that probably it
+      // doesn't have header or there are more than one RNSNavigationController which is invalid) we don't want to
+      // return anything.
+      return nil;
+    }
   }
 
-  return navctr.navigationBar.frame.size.height;
+  return navctr;
 }
 
-- (CGFloat)getNavigationBarInsetIsModal:(BOOL)isModal
+- (CGFloat)calculateHeaderHeightIsModal:(BOOL)isModal
 {
-#if TARGET_OS_TV
-  // On TVOS there's no inset of navigation bar.
-  return 0;
-#endif // TARGET_OS_TV
-  UINavigationController *navctr = self.navigationController;
+  UINavigationController *navctr = [self getVisibleNavigationControllerIsModal:isModal];
 
-  // In case where screen is a modal, we want to calculate childViewController's
-  // navigation bar inset instead of the navigation controller from RNSScreen.
-  if (isModal && self.assertModalHierarchy) {
-    navctr = self.childViewControllers[0];
+  if (navctr == nil || navctr.navigationBarHidden) {
+    return 0;
   }
 
-  return navctr.navigationBar.frame.origin.y;
-}
+  CGFloat navbarHeight = navctr.navigationBar.frame.size.height;
+#if !TARGET_OS_TV
+  CGFloat navbarInset = navctr.navigationBar.frame.origin.y;
+#else
+  // On TVOS there's no inset of navigation bar.
+  CGFloat navbarInset = 0;
+#endif // !TARGET_OS_TV
 
-- (CGFloat)calculateHeaderHeightIsModal:(BOOL)isModal
-{
-  CGFloat navbarHeight = [self getNavigationBarHeightIsModal:isModal];
-  CGFloat navbarInset = [self getNavigationBarInsetIsModal:isModal];
   return navbarHeight + navbarInset;
 }