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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
bool send_to_all,
                                        int32_t frame_id,
                                        const std::string& channel,
                                        v8::Local<v8::Value> args) {
  v8::Isolate* isolate = JavascriptEnvironment::GetIsolate();
  blink::CloneableMessage message;
  if (!gin::ConvertFromV8(isolate, args, &message)) {
    isolate->ThrowException(v8::Exception::Error(
        gin::StringToV8(isolate, "Failed to serialize arguments")));
    return false;
  }
  auto frames = ontents()->GetAllFrames();
  auto iter = std::find_if(frames.begin(), frames.end(), [frame_id](auto* f) {
    return f->GetRoutingID() == frame_id;
  });
  if (iter == frames.end())
    return false;
  if (!(*iter)->IsRenderFrameLive())
    return false;
  mojo::AssociatedRemote<mojom::ElectronRenderer> electron_renderer;
  (*iter)->GetRemoteAssociatedInterfaces()->GetInterface(&electron_renderer);
  electron_renderer->Message(internal, send_to_all, channel, std::move(message),
                             0 /* sender_id */);
  return true;
}
void WebContents::SendInputEvent(v8::Isolate* isolate,