FIX missing column when module was installed before standard integration

htdocs/install/mysql/migration/3.7.0-3.8.0.sql

@@ -797,6 +797,7 @@ ALTER TABLE llx_societe_remise_except MODIFY COLUMN description text NOT NULL;
 update llx_opensurvey_sondage set format = 'D' where format = 'D+';
 update llx_opensurvey_sondage set format = 'A' where format = 'A+';
 
+ALTER TABLE llx_propal_merge_pdf_product ADD COLUMN lang varchar(5) DEFAULT NULL;
 
 --Deal with holidays_user that do not have rowid
 -- Disabled: too dangerous patch. rowid is a primary key. How is it possible to have no rowid ?