Item.retain_sample is validated against any company having one configured,
since Item is not company-scoped. The transaction company may still not be,
in which case get_batch_qty received warehouse=None and returned its batch
list, which was then compared numerically -> TypeError.
Resolve company -> retention warehouse through one helper that throws a
clear message instead, covering both the sample stock entry and the
whitelisted quantity validation.
455251abe1