Fix incorrect handling of UNKNOWN captive portal state by supervised user creation screen.

BUG=480505
R=nkostylev@chromium.org

Review URL: https://codereview.chromium.org/1100363002

Cr-Commit-Position: refs/heads/master@{#326671}

chrome/browser/chromeos/login/supervised/supervised_user_creation_screen.cc

@@ -156,7 +156,8 @@ void SupervisedUserCreationScreen::OnPortalDetectionCompleted(
   if (state.status == NetworkPortalDetector::CAPTIVE_PORTAL_STATUS_ONLINE) {
     get_base_screen_delegate()->HideErrorScreen(this);
     histogram_helper_->OnErrorHide();
-  } else {
+  } else if (state.status !=
+             NetworkPortalDetector::CAPTIVE_PORTAL_STATUS_UNKNOWN) {
     on_error_screen_ = true;
     ErrorScreen* screen = get_base_screen_delegate()->GetErrorScreen();
     ConfigureErrorScreen(screen, network, state.status);