Fix missing identifier from r23520

git-svn-id: svn+ssh://svn.gnucash.org/repo/gnucash/trunk@23521 57a11ea4-9604-0410-9ed3-97b8803252fd
Bug 632588 - Scrub doesn't fix missing currency

So assign the currency from the first split (that belongs to an account.)

git-svn-id: svn+ssh://svn.gnucash.org/repo/gnucash/trunk@23522 57a11ea4-9604-0410-9ed3-97b8803252fd