use pushback instead of index operator

Author: DellaBitta

auth/integration_test/src/integration_test.cc

@@ -1448,6 +1448,7 @@ TEST_F(FirebaseAuthTest, TestAuthPersistenceWithEmailSignin) {
   // Save the old provider ID list so we can make sure it's the same once
   // it's loaded again.
   std::vector<std::string> prev_provider_data_ids;
+  LogError("about to query provider data size\n");
   LogError("user.provider_data().size(): %d\n", user.provider_data().size());
   for (int i = 0; i < user.provider_data().size(); i++) {
     prev_provider_data_ids.push_back(user.provider_data()[i].provider_id());

auth/src/desktop/user_desktop.cc

@@ -1212,7 +1212,7 @@ std::vector<UserInfoInterface> User::provider_data() const {
       user_info_impl.photo_url = deprecated_provider_data[i]->photo_url();
       user_info_impl.provider_id = deprecated_provider_data[i]->provider_id();
       user_info_impl.phone_number = deprecated_provider_data[i]->phone_number();
-      provider_data[i] = UserInfoInterfaceImpl(user_info_impl);
+      provider_data.push_back(UserInfoInterfaceImpl(user_info_impl));
     }
   }
   printf("DEDB provider_data return length: %d\n", provider_data.size());