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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
options.Get("color", &print_color);
  auto const color_model = print_color ? printing::mojom::ColorModel::kColor
                                       : printing::mojom::ColorModel::kGray;
  settings.SetIntKey(printing::kSettingColor, static_cast<int>(color_model));
   Is the orientation landscape or portrait.
  bool landscape = false;
  options.Get("landscape", &landscape);
  settings.SetBoolKey(printing::kSettingLandscape, landscape);
   We set the default to the system's default printer and only update
   if at the Chromium level if the user overrides.
   Printer device name as opened by the OS.
  base::string16 device_name;
  options.Get("deviceName", &device_name);
  if (!device_name.empty() && !IsDeviceNameValid(device_name)) {
    gin_helper::ErrorThrower(args->isolate())
        .ThrowError("webContents.print(): Invalid deviceName provided.");
    return;
  }
  int scale_factor = 100;
  options.Get("scaleFactor", &scale_factor);
  settings.SetIntKey(printing::kSettingScaleFactor, scale_factor);
  int pages_per_sheet = 1;
  options.Get("pagesPerSheet", &pages_per_sheet);
  settings.SetIntKey(printing::kSettingPagesPerSheet, pages_per_sheet);
   True if the user wants to print with collate.
  bool collate = true;
  options.Get("collate", &collate);
  settings.SetBoolKey(printing::kSettingCollate, collate);
   The number of individual copies to print
  int copies = 1;