Bug 677489 - Critical error reported when initializing an Invoice

Apply BeginEdit() and CommitEdit() functions in Invoice class to resolve invoice creation issue.

Author: Tom Lofts <dev@loftx.co.uk>

git-svn-id: svn+ssh://svn.gnucash.org/repo/gnucash/trunk@23763 57a11ea4-9604-0410-9ed3-97b8803252fd