* Electron version: 1.4.15 (probably older versions too).
* Operating system: macOS 10.12.2

When Quick Look is launched by right-clicking a file in a file dialog, clicking its close button doesn't work (and there's an audible beep), and after enough clicking around frequently it crashes. I suspect the same thing would happen using `dialog.showOpenDialog` presented as a sheet, but I haven't tested.

Minimal app to reproduce:
```js
const {app, BrowserWindow} = require('electron')

app.on('ready', () => {
  const win = new BrowserWindow({width: 300, height: 100})
  win.loadURL('data:text/html,<input type="file">')
})
```

Example:
![quicklook](https://cloud.githubusercontent.com/assets/5355/22160125/06120964-df12-11e6-86db-996f2233bf5e.gif)

Crash log: https://gist.github.com/javan/4c19dddd73b0581e60f6baf3b75d4dd8
atom/browser/web_dialog_helper.cc
int request_id,
                                         const base::FilePath& dir) {
  int types = base::FileEnumerator::FILES |
              base::FileEnumerator::DIRECTORIES |
              base::FileEnumerator::INCLUDE_DOT_DOT;
  base::FileEnumerator file_enum(dir, false, types);
  base::FilePath path;
  std::vector<base::FilePath> paths;
  while (!(path = file_enum.Next()).empty())
    paths.push_back(path);
  web_contents->GetRenderViewHost()->DirectoryEnumerationFinished(
      request_id, paths);
}
}