Skip if no content has begun loading yet. Can't check with

[github-actions[bot]]

ICoreWebView2::get_Source because it returns "about:blank".

https://github.com/arturo-lang/arturo/blob/135fdd90eb88beea0e8a44eacc40ab01f1076180/src/extras/webview/webview-unix.cc#L4136

                   SWP_NOZORDER | SWP_NOACTIVATE | SWP_NOMOVE |
                       SWP_FRAMECHANGED);
    }
    return {};
  }

  noresult navigate_impl(const std::string &url) override {
    auto wurl = widen_string(url);
    m_webview->Navigate(wurl.c_str());
    return {};
  }

  noresult eval_impl(const std::string &js) override {
    // TODO: Skip if no content has begun loading yet. Can't check with
    //       ICoreWebView2::get_Source because it returns "about:blank".
    auto wjs = widen_string(js);
    m_webview->ExecuteScript(wjs.c_str(), nullptr);
    return {};
  }

  noresult set_html_impl(const std::string &html) override {
    m_webview->NavigateToString(widen_string(html).c_str());
    return {};
  }

  user_script add_user_script_impl(const std::string &js) override {
    auto wjs = widen_string(js);
    std::wstring script_id;
    bool done{};
    webview2_user_script_added_handler handler{[&](HRESULT res, LPCWSTR id) {
      if (SUCCEEDED(res)) {
        script_id = id;
      }
      done = true;
    }};
    auto res =
        m_webview->AddScriptToExecuteOnDocumentCreated(wjs.c_str(), &handler);
    if (SUCCEEDED(res)) {
      // Sadly we need to pump the even loop in order to get the script ID.
      while (!done) {
        deplete_run_loop_event_queue();
      }
    }
    // TODO: There's a non-zero chance that we didn't get the script ID.
    //       We need to convey the error somehow.
    return user_script{js, std::unique_ptr<user_script::impl>{
                               new user_script::impl{script_id, wjs}}};
  }

  void
  remove_all_user_scripts_impl(const std::list<user_script> &scripts) override {
    for (const auto &script : scripts) {
      const auto &id = script.get_impl().get_id();
      m_webview->RemoveScriptToExecuteOnDocumentCreated(id.c_str());
    }
  }

  bool are_user_scripts_equal_impl(const user_script &first,
                                   const user_script &second) override {
    const auto &first_id = first.get_impl().get_id();
    const auto &second_id = second.get_impl().get_id();
    return first_id == second_id;
  }

private:
  noresult embed(HWND wnd, bool debug, msg_cb_t cb) {
    std::atomic_flag flag = ATOMIC_FLAG_INIT;
    flag.test_and_set();