X2ManyFieldDialogs with no sheets were badly styled since the rewriting of the form view in OWL (see https://github.com/odoo/odoo/commit/48ef812a635f70571b395f82). For instance paddings were not set and this would make the dialog content touch its borders. We fix that. closes odoo/odoo#98072 Related: odoo/enterprise#30411 Signed-off-by: Samuel Degueldre <sad@odoo.com>