gnucash maint: Fix crash when there's no TRANS_READ_ONLY_REASON slot.

[John Ralls]

Updated	 via  https://github.com/Gnucash/gnucash/commit/a19dcc7b (commit)
	from  https://github.com/Gnucash/gnucash/commit/b2d99615 (commit)



commit a19dcc7bd4b4c2a64f905968b8db523fee44c31d
Author: John Ralls <jralls at ceridwen.us>
Date:   Sun Sep 9 15:02:53 2018 -0700

    Fix crash when there's no TRANS_READ_ONLY_REASON slot.
    
    Unsetting an empty g_value raises a fatal error, causing tests to fail
    in some environments.
    
    g_free() handles NULLs itself, no need to protect it.



Summary of changes:
 libgnucash/engine/Transaction.c | 18 ++++++++----------
 1 file changed, 8 insertions(+), 10 deletions(-)