Explicitly call out if initialized via boolean

Author: adamschlesinger

com.onesignal.unity.android/Runtime/OneSignalAndroidInit.cs

@@ -34,7 +34,7 @@ namespace OneSignalSDK {
     /// </summary>
     internal static class OneSignalAndroidInit {
         [RuntimeInitializeOnLoadMethod] public static void Init() {
-            if (string.IsNullOrEmpty(OneSignal.AppId))
+            if (!OneSignal.DidInitialize) 
                 OneSignal.Default = new OneSignalAndroid();
         }
     }

com.onesignal.unity.core/Runtime/OneSignal.Internal.cs

@@ -32,10 +32,12 @@
 namespace OneSignalSDK {
     public abstract partial class OneSignal {
         internal static string AppId { get; private set; }
+        internal static bool DidInitialize { get; private set; }
         internal static event Action<string> OnInitialize;
 
         protected static void _completedInit(string appId) {
-            AppId = appId;
+            AppId         = appId;
+            DidInitialize = true;
             OnInitialize?.Invoke(AppId);
         }
 

com.onesignal.unity.ios/Runtime/OneSignalIOSInit.cs

@@ -34,7 +34,7 @@ namespace OneSignalSDK {
     /// </summary>
     internal static class OneSignalIOSInit {
         [RuntimeInitializeOnLoadMethod] public static void Init() {
-            if (string.IsNullOrEmpty(OneSignal.AppId))
+            if (!OneSignal.DidInitialize) 
                 OneSignal.Default = new OneSignalIOS();
         }
     }