Use find_by_branch when possible for wizards

When running the advanced sellable search for wizards (eg, purchase, sale,
transfer, etc..), use find_by_branch when its available, so that the resuls
show the stock for the current branch only.

Fixes: http://bugs.async.com.br/show_bug.cgi?id=5591
Change-Id: Id57ea7115860c5a2fe892f10d2271363e5f51299