gnucash maint: Correct detection of marker commodity splits.

[John Ralls]

Updated	 via  https://github.com/Gnucash/gnucash/commit/8d904c12 (commit)
	from  https://github.com/Gnucash/gnucash/commit/5f0cb073 (commit)



commit 8d904c1209d3973f5f2bbf948c0c88c436dbdebc
Author: John Ralls <jralls at ceridwen.us>
Date:   Thu Dec 17 16:38:35 2015 -0800

    Correct detection of marker commodity splits.
    
    The splits don't have an amount until after the formula is parsed, so
    use the absence of both a credit and debit formula to indicate a marker.



Summary of changes:
 src/app-utils/gnc-sx-instance-model.c | 51 ++++++++++++++++++-----------------
 1 file changed, 26 insertions(+), 25 deletions(-)