fix(ios): UIViewControllerHierarchyInconsistency error (#432)

Author: troZee

ios/ReactNativePageView.m

@@ -147,7 +147,13 @@ - (void)shouldDismissKeyboard:(NSString *)dismissKeyboard {
 - (void)setupInitialController {
     UIView *initialView = self.reactSubviews[self.initialPage];
     if (initialView) {
-        UIViewController *initialController = [[UIViewController alloc] initWithView:initialView];
+        UIViewController *initialController = nil;
+        if (initialView.reactViewController) {
+            initialController = initialView.reactViewController;
+        } else {
+            initialController = [[UIViewController alloc] initWithView:initialView];
+        }
+
         [self.cachedControllers addObject:initialController];
 
         [self setReactViewControllers:self.initialPage
@@ -250,7 +256,11 @@ - (UIViewController *)findAndCacheControllerForView:(UIView *)viewToDisplay {
         controllerToDisplay = current;
     }
     if (!controllerToDisplay) {
-        controllerToDisplay = [[UIViewController alloc] initWithView:viewToDisplay];
+        if (viewToDisplay.reactViewController) {
+            controllerToDisplay = viewToDisplay.reactViewController;
+        } else {
+            controllerToDisplay = [[UIViewController alloc] initWithView:viewToDisplay];
+        }
     }
     [self.cachedControllers addObject:controllerToDisplay];