Fixed ADM registration crash possibly from service restarts

Author: jkasten2

OneSignalSDK/onesignal/src/main/java/com/onesignal/ADMMessageHandler.java

@@ -57,7 +57,7 @@ protected void onMessage(Intent intent) {
 
    @Override
    protected void onRegistered(String newRegistrationId) {
-      OneSignal.Log(OneSignal.LOG_LEVEL.INFO, "ADM registartion ID: " + newRegistrationId);
+      OneSignal.Log(OneSignal.LOG_LEVEL.INFO, "ADM registration ID: " + newRegistrationId);
       PushRegistratorADM.fireCallback(newRegistrationId);
    }
 

OneSignalSDK/onesignal/src/main/java/com/onesignal/PushRegistratorADM.java

@@ -63,6 +63,8 @@ public void run() {
    }
 
    public static void fireCallback(String id) {
+      if (registeredCallback == null)
+         return;
       callbackSuccessful = true;
       registeredCallback.complete(id, 1);
    }