address PR comments

* Move clearing local data inside the `if response` block.
* We don't know what it would mean to have a successful yet `nil` response, or if this can even happen, so it is better to not make any local changes in that case.

Author: nan-li

iOS_SDK/OneSignalSDK/OneSignalUser/Source/OSUserRequests.swift

@@ -266,10 +266,9 @@ class OSUserExecutor {
         }
 
         OneSignalClient.shared().execute(request) { response in
-            // Clear local data in preparation for hydration
-            OneSignalUserManagerImpl.sharedInstance.clearUserData()
-
             if let response = response {
+                // Clear local data in preparation for hydration
+                OneSignalUserManagerImpl.sharedInstance.clearUserData()
                 parseFetchUserResponse(response: response, identityModel: request.identityModel, originalPushToken: OneSignalUserManagerImpl.sharedInstance.token)
             }
         } onFailure: { _ in