FormViewHelper generates empty fragment for action uri due to preg_replace and missing conditino

[sorenmalling]

The current action uri can get a section added (the #[section] value of a uri).

This is done by check if the argument has a value (empty string included) and with preg_replace, the value is added.

Since we get a UriInterface object, we can use the withFragment instead, but it requires a stricter check for the section value, since it does not accept a empty string