Can the extension of the residence permit of a family member – who was permitted to join the principal person entitled at a time when the latter was not duly registered as belonging to the labour force – at a date on which the principal person entitled, with whom the family member is lawfully resident, has become an employed person be regarded as constituting an ‘authorisation to join’ for the purposes of Article 7 of EEC-Turkey Association Council Decision No 1/80 of 19‍ September 1980?