<!--  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
ontents()->SelectAll();
}
void WebContents::Unselect() {
  ontents()->CollapseSelection();
}
void WebContents::Replace(const base::string16& word) {
  ontents()->Replace(word);
}
void WebContents::ReplaceMisspelling(const base::string16& word) {
  ontents()->ReplaceMisspelling(word);
}
uint32_t WebContents::FindInPage(gin::Arguments* args) {
  base::string16 search_text;
  if (!args->GetNext(&search_text) || search_text.empty()) {
    gin_helper::ErrorThrower(args->isolate())
        .ThrowError("Must provide a non-empty search content");
    return 0;
  }
  uint32_t request_id = ++find_in_page_request_id_;
  gin_helper::Dictionary dict;
  auto options = blink::mojom::FindOptions::New();
  if (args->GetNext(&dict)) {
    dict.Get("forward", &options->forward);
    dict.Get("matchCase", &options->match_case);
    dict.Get("findNext", &options->new_session);
  }
  ontents()->Find(request_id, search_text, std::move(options));
  return request_id;
}
void WebContents::StopFindInPage(content::StopFindAction action) {