[BUGFIX] Check powermail JS validation in submit race-condition handler

[kitzberger]

Problem

The #submitListener race-condition handler calls form.submit() directly, which bypasses powermail's JavaScript validation submit event listener entirely (form.submit() does not fire the submit event).

The existing reportValidity() check (added in 8b96e25) only covers native HTML5 validation, but always returns true when the form has a novalidate attribute — i.e. when native validation is disabled via TypoScript (validation.native = 0).

This means: when using only JS client validation (validation.client = 1, validation.native = 0), powermail's field-level validation errors are shown on blur, but clicking submit still sends the form to the server.

Fix

• Adds a check for the powermail_form_error CSS class (set by powermail's JS validation framework when any field has errors) alongside the existing reportValidity() check.
• Also adds the validation check to the direct-submit path (when no form element is focused), which previously had no validation guard at all.

Both checks are extracted into a #hasValidationErrors() helper method.

Co-Authored-By: Oz oz-agent@warp.dev