Guarantee that messageView is a subview of OSInAppMessageVC

There is swiftUI crash where addConstraintsForMessage can be called without messageView being a subview of OSInAppMessageViewController's view.  This is likely happening because viewWillTransitionToSize is being called before setupInitialMessageUI. Neither the crash reporters nor OneSignal have been able to reproduce the crash, but it is safe to always add messageView as a subview if it is not already.

Author: emawby

iOS_SDK/OneSignalSDK/Source/OSInAppMessageViewController.m

@@ -280,6 +280,11 @@ Sets up the message view in its initial (hidden) position
 - (void)addConstraintsForMessage {
     [OneSignal onesignal_Log:ONE_S_LL_VERBOSE message:@"Setting up In-App Message Constraints"];
 
+    if (![self.view.subviews containsObject:self.messageView]) {
+        [OneSignal onesignal_Log:ONE_S_LL_VERBOSE message:@"addConstraintsForMessage: messageView is not a subview of OSInAppMessageViewController"];
+        [self.view addSubview:self.messageView];
+    }
+    
     // Initialize the anchors that describe the edges of the view, such as the top, bottom, etc.
     NSLayoutAnchor *top = self.view.topAnchor,
                    *bottom = self.view.bottomAnchor,