<!--  As an open source project with a dedicated but small maintainer team, it can sometimes take a long time for issues to be addressed so please be patient and we will get back to you as soon as we can.
-->

### Preflight Checklist
<!-- Please ensure you've completed the following steps by replacing [ ] with [x]-->

* [x] I have read the [Contributing Guidelines](https://github.com/electron/electron/blob/master/CONTRIBUTING.md) for this project.
* [x] I agree to follow the [Code of Conduct](https://github.com/electron/electron/blob/master/CODE_OF_CONDUCT.md) that this project adheres to.
* [x] I have searched the issue tracker for an issue that matches the one I want to file, without success.

### 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
const gfx::Size& pref_size) {
  Emit("preferred-size-changed", pref_size);
}
bool WebContents::CanOverscrollContent() {
  return false;
}
content::ColorChooser* WebContents::OpenColorChooser(
    content::WebContents* ontents,
    SkColor color,
    const std::vector<blink::mojom::ColorSuggestionPtr>& suggestions) {
#if BUILDFLAG(ENABLE_COLOR_CHOOSER)
  return chrome::ShowColorChooser(ontents, color);
#else
  return nullptr;
#endif
}
void WebContents::RunFileChooser(
    content::RenderFrameHost* render_frame_host,
    scoped_refptr<content::FileSelectListener> listener,
    const blink::mojom::FileChooserParams& params) {
  if (!web_dialog_helper_)
    web_dialog_helper_ =
        std::make_unique<WebDialogHelper>(owner_window(), offscreen_);
  web_dialog_helper_->RunFileChooser(render_frame_host, std::move(listener),
                                     params);
}
void WebContents::EnumerateDirectory(