Fix validation message in full width layout

[danieleugoletti]

In a Flexible with require rules and fullWidth property, the validation message is not displayed
This PR fix the issue.

ie.

Flexible::make('Flexible', 'data')
    ->addLayout('My layout', 'my-layout', [
        Text::make('Text', 'text'),
    ])
    ->fullWidth()
    ->rules('required');

[toonvandenbos]

Thank you @danieleugoletti !