[sfnt] Avoid nullptr dereference in reading malformed 'COLR' v1 table. Fixes https://bugs.chromium.org/p/chromium/issues/detail?id=1408044. * src/sfnt/ttcolr.c (tt_face_load_colr): When the 'COLR' v1 table header is too small, don't deallocate delta set index map structures.