Validation ignores storagePid given by Plugin

[Bunnyfield]

When running client side validation for a user registration used on a multidomain site with different user storage folders, the validation "uniqueInPage" fails, because the plugin setting is ignored and the default storagePid configured in plugin.tx_femanager.persistence.storagePid is used instead.

While there is a workaround by defining the same default storagePid as given by the plugin for each different plugin on the site, the default should actually be used as a fallback only if there is no ID given by the plugin at all.