[Coverity 1666142] Dereference null return value in acouticid.c

If the function actually returns a null value, a null pointer dereference will occur.

In parse_recordings: Return value of function which returns null is dereferenced without checking (CWE-476)

      17. returned_null: json_get_array returns NULL (checked 8 out of 9 times).[show details]
      18. var_assigned: Assigning: artists = NULL return value from json_get_array.
 79        const struct json_array *artists = json_get_array(&recordnode->object,
 80                                                          "artists");
     
CID 1666142: (#1 of 1): Dereference null return value (NULL_RETURNS)
19. dereference: Dereferencing a pointer that might be NULL artists when calling parse_artists.[show details]
 81        parse_artists( artists, record );