gnucash maint: [register.scm] prevent crash on running report on empty book

[Christopher Lam]

Updated	 via  https://github.com/Gnucash/gnucash/commit/35374158 (commit)
	from  https://github.com/Gnucash/gnucash/commit/c7b0aca4 (commit)



commit 3537415889ff87f24a971b149c6013af2b594027
Author: Christopher Lam <christopher.lck at gmail.com>
Date:   Fri Sep 11 18:43:34 2020 +0800

    [register.scm] prevent crash on running report on empty book



Summary of changes:
 gnucash/report/reports/standard/register.scm | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)