SEQUENCE_QUALITY binding

I extended `primer3_test.py` to use `SEQUENCE_QUALITY`. That blew up the `bindings` but not the `wrappers`. Turns out a `NULL` pointer was being passed to the `DICT_GET_AND_COPY_ARRAY` macro to receive the length of the `SEQUENCE_QUALITY` array. I changed the relevant use of the macro to store directly into `sa->n_quality` (which it only does if `SEQUENCE_QUALITY` is actually in the argument dictionary).