### Preflight Checklist
* [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
```js
let ret = shell.openItem('file:///noexistent');
console.log(ret);
```
`ret` is always `true` on Linux even if opening fails, e.g.
```sh
xdg-open 'file:///noexistent'
echo $?
```
Shows nonzero error code.

* **Electron Version:**
  * v6.0.11
* **Operating System:**
  *Linux / Ubuntu 16.04 x64

### Expected Behavior
`ret` should be `false`, if `xdg-open` returns non-zero code.

Optional: It would be very nice if the `xdg-open` error (catch stderr) would be displayed in `dialog.showErrorBox` if it returns non-zero code. Just take care that `xdg-open` may write some warnings to stderr even if it returns 0.

shell/common/platform_util_win.cc
FOF_NO_UI | FOFX_ADDUNDORECORD | FOF_NOERRORUI | FOF_SILENT |
            FOFX_SHOWELEVATIONPROMPT | FOFX_RECYCLEONDELETE)))
      return false;
  } else {
    
    if (FAILED(pfo->SetOperationFlags(FOF_NO_UI | FOF_ALLOWUNDO |
                                      FOF_NOERRORUI | FOF_SILENT |
                                      FOFX_SHOWELEVATIONPROMPT)))
      return false;
  }
  
  Microsoft::WRL::ComPtr<IShellItem> delete_item;
  if (FAILED(SHCreateItemFromParsingName(
          path.value().c_str(), NULL,
          IID_PPV_ARGS(delete_item.GetAddressOf()))))
    return false;
  Microsoft::WRL::ComPtr<IFileOperationProgressSink> delete_sink(
      new DeleteFileProgressSink);
  if (!delete_sink)
    return false;
  
  
  return SUCCEEDED(pfo->DeleteItem(delete_item.Get(), delete_sink.Get())) &&
         SUCCEEDED(pfo->PerformOperations());
}
void Beep() {
  MessageBeep(MB_OK);
}
}