How many horror movies were made by the worst directors?
d_quality = 5 refers to direct the best, d_quality = 0 refers to direct the worst
SELECT COUNT(T1.movieid) FROM movies2directors AS T1 INNER JOIN movies AS T2 ON T1.movieid = T2.movieid INNER JOIN directors AS T3 ON T1.directorid = T3.directorid WHERE T1.genre = 'horror' AND T3.d_quality = 0