Check and pop EXTERNAL_USER_ID_AUTH_HASH every time we persistState

- Every time we persistState, we check if the syncValues has an EXTERNAL_USER_ID_AUTH_HASH that is a candidate to be popped.
- It is removed if either the EXTERNAL_USER_ID is "" (empty string) or not in the syncValues.
- In some cases, when we set the external user ID to "", the EXTERNAL_USER_ID_AUTH_HASH is in the syncValues while the EXTERNAL_USER_ID is not but we want to pop the EXTERNAL_USER_ID_AUTH_HASH

Author: nan-li

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

@@ -15,6 +15,7 @@
 
 import static com.onesignal.UserStateSynchronizer.APP_ID;
 import static com.onesignal.UserStateSynchronizer.EMAIL_AUTH_HASH_KEY;
+import static com.onesignal.UserStateSynchronizer.EXTERNAL_USER_ID;
 import static com.onesignal.UserStateSynchronizer.EXTERNAL_USER_ID_AUTH_HASH;
 import static com.onesignal.UserStateSynchronizer.SMS_AUTH_HASH_KEY;
 
@@ -318,6 +319,18 @@ private void loadState() {
 
     void persistState() {
         synchronized(LOCK) {
+            // pop the EXTERNAL_USER_ID_AUTH_HASH if in process of removing external user ID
+            // external_user_id is either "" or not present
+            try {
+                if (syncValues.has(EXTERNAL_USER_ID_AUTH_HASH) &&
+                        ((syncValues.has(EXTERNAL_USER_ID) && syncValues.get(EXTERNAL_USER_ID).toString() == "") || !syncValues.has(EXTERNAL_USER_ID))) {
+                    syncValues.remove(EXTERNAL_USER_ID_AUTH_HASH);
+                    // the auth_hash is popped above but external user id may still remain as ""
+                }
+            } catch (JSONException e) {
+                e.printStackTrace();
+            }
+
             OneSignalPrefs.saveString(OneSignalPrefs.PREFS_ONESIGNAL,
                     OneSignalPrefs.PREFS_ONESIGNAL_USERSTATE_SYNCVALYES_ + persistKey, syncValues.toString());
             OneSignalPrefs.saveString(OneSignalPrefs.PREFS_ONESIGNAL,