coalesce GILless sections in new_buffersize (#5059)

830daae1c82ed33deef0086b7b6323e5be0b0cc8 added some new GIL-releasing to new_buffersize. This is fine, but it's better to avoid reacquiring the GIL for as long as possible. Also, it should use FILE_(BEGIN|END)_ALLOW_THREADS to avoid having the file closed from under it.
1 file changed