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### Issue Details
webContents.fromId() for non existing id (e.g. removed webview) causes segmentation fault in Electron 11.
In Electron 9 & 10 null was returned.
Same problem on Windows and macOS Catalina 

* **Electron Version:**
  * 11.0.1
* **Operating System:**
  * macOS 11.0.1
* **Last Known Working Electron version:**
  * 10.1.6

### Expected Behavior
<!-- A clear and concise description of what you expected to happen. -->
webContents.fromId() returns null for non existing id

### Actual Behavior
<!-- A clear and concise description of what actually happened. -->
Segmentation fault

### To Reproduce
https://gist.github.com/larssvensby/071353ec109c4975fd28b5a4b1dc7ad5

### Screenshots
<!-- If applicable, add screenshots to help explain your problem. -->

### Additional Information
<!-- Add any other context about the problem here. -->

shell/browser/api/electron_api_web_contents.cc
range.SetIntKey(printing::kSettingPageRangeTo, to + 1);
        page_range_list.Append(std::move(range));
      } else {
        continue;
      }
    }
    if (!page_range_list.GetList().empty())
      settings.SetPath(printing::kSettingPageRange, std::move(page_range_list));
  }
   Duplex type user wants to use.
  printing::mojom::DuplexMode duplex_mode =
      printing::mojom::DuplexMode::kSimplex;
  options.Get("duplexMode", &duplex_mode);
  settings.SetIntKey(printing::kSettingDuplexMode,
                     static_cast<int>(duplex_mode));
   We've already done necessary parameter sanitization at the
   JS level, so we can simply pass this through.
  base::Value media_size(base::Value::Type::DICTIONARY);
  if (options.Get("mediaSize", &media_size))
    settings.SetKey(printing::kSettingMediaSize, std::move(media_size));
   Set custom dots per inch (dpi)
  gin_helper::Dictionary dpi_settings;
  int dpi = 72;
  if (options.Get("dpi", &dpi_settings)) {
    int horizontal = 72;
    dpi_settings.Get("horizontal", &horizontal);
    settings.SetIntKey(printing::kSettingDpiHorizontal, horizontal);
    int vertical = 72;
    dpi_settings.Get("vertical", &vertical);
    settings.SetIntKey(printing::kSettingDpiVertical, vertical);