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### Issue Details

* **Electron Version:**
  * 5.0.0
* **Operating System:**
  * macOS 10.14.4
* **Last Known Working Electron version:**:
  * 4.1.4

### Expected Behavior
Quitting while a debugger is attached to the process results in the application exiting without error.

### Actual Behavior
Qutting while a debugger is still attached results in the application crashing and macOS showing its crash report dialog.

### To Reproduce

1. Run electron with `--inspect=9229` or `--inspect-brk=9229`.
2. Attach with a debugger (such as Visual Studio Code).
3. Quit electron without detaching.

Below is a repo that reproduces the issue:
[Repo that reproduces the issue](https://github.com/kpes/electron5attachquitcrash)

```sh
$ git clone https://github.com/kpes/electron5attachquitcrash.git
$ npm install
```

atom/browser/node_debugger.cc
if (inspector == nullptr)
    return;
  std::vector<std::string> args;
  for (auto& arg : base::CommandLine::ForCurrentProcess()->argv()) {
#if defined(OS_WIN)
    args.push_back(base::UTF16ToUTF8(arg));
#else
    args.push_back(arg);
#endif
  }
  node::DebugOptions options;
  node::options_parser::DebugOptionsParser options_parser;
  std::vector<std::string> exec_args;
  std::vector<std::string> v8_args;
  std::vector<std::string> errors;
  options_parser.Parse(&args, &exec_args, &v8_args, &options,
                       node::options_parser::kDisallowedInEnvironment, &errors);
  if (!errors.empty()) {
    
    LOG(ERROR) << "Error parsing node options: "
               << base::JoinString(errors, " ");
  }
  const char* path = "";
  if (inspector->Start(path, options,
                       std::make_shared<node::HostPort>(options.host_port),
                       true ))
    DCHECK(env_->inspector_agent()->IsListening());
}
}