Fix sonata_formatter_type_widget with single format option template rendering

[azlotnikov]

Subject

Resolve Issue "FormatterType is not working with single format option"

I am targeting this branch, because it's a bug fix.

Closes #734

Changelog

### Fixed
- Fix sonata_formatter_type_widget with single format option template rendering

[VincentLanglet]

Thanks for the bugfix. Do you think you can add a test for this case ? @azlotnikov

[azlotnikov]

Thanks for the bugfix. Do you think you can add a test for this case ? @azlotnikov

Done, but I think it should improved a little bit, so dont merge pls.

[azlotnikov]

@VincentLanglet Seems ok now)

[VincentLanglet]

Thanks