Check publication exists before inserting author record

DBD::Pg::db do failed: ERROR:  insert or update on table "mm_user_publications_author" violates foreign key constraint "mm_user_publications_author_publication_id_fkey"
DETAIL:  Key (publication_id)=(1103155) is not present in table "publications". at /usr/local/elements-importer/Elements/Database.pm line 196.

Fix is probably just to check with existing function publicationIdExistsInDB($id) before trying to insert in add_mm_author().