gnucash stable: [Transaction.cpp] use qof_instance kvp API for Time64, with bugfix

[Christopher Lam]

Updated	 via  https://github.com/Gnucash/gnucash/commit/ab04715c (commit)
	from  https://github.com/Gnucash/gnucash/commit/985f5918 (commit)



commit ab04715c910d63e17c4711fca965915da3e7fc7c
Author: Christopher Lam <christopher.lck at gmail.com>
Date:   Sat Jun 28 17:58:40 2025 +0800

    [Transaction.cpp] use qof_instance kvp API for Time64, with bugfix
    
    fixes bug whereby xaccTransRetDateDue returns 0 if the kvp time64
    stored is 0.



Summary of changes:
 libgnucash/engine/Transaction.cpp            | 19 +++----------------
 libgnucash/engine/qofinstance.cpp            |  2 ++
 libgnucash/engine/test/utest-Transaction.cpp |  3 +--
 3 files changed, 6 insertions(+), 18 deletions(-)