### 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
if (FAILED(hr)) {
    ui::win::OpenFolderViaShell(dir);
    return;
  }
  const ITEMIDLIST* highlight[] = {file_item};
  hr = SHOpenFolderAndSelectItems(dir_item, base::size(highlight), highlight,
                                  NULL);
  if (FAILED(hr)) {
    
    
    
    if (hr == ERROR_FILE_NOT_FOUND) {
      ShellExecute(NULL, L"open", dir.value().c_str(), NULL, NULL, SW_SHOW);
    } else {
      LOG(WARNING) << " " << __func__ << "(): Can't open full_path = \""
                   << full_path.value() << "\""
                   << " hr = " << logging::SystemErrorCodeToString(hr);
      ui::win::OpenFolderViaShell(dir);
    }
  }
}
}  
namespace platform_util {
void ShowItemInFolder(const base::FilePath& full_path) {
  base::CreateCOMSTATaskRunner(
      {base::ThreadPool(), base::MayBlock(), base::TaskPriority::USER_BLOCKING})
      ->PostTask(FROM_HERE,
                 base::BindOnce(&ShowItemInFolderOnWorkerThread, full_path));
}
bool OpenItem(const base::FilePath& full_path) {