Bug 14591: (QA follow-up) Optimize DateTime passing

Bug 14591: (QA follow-up) Optimize DateTime passing

We were passing around possibly undefined $return_date variables from
AddReturn and then instantiating a new DateTime object as a default for
each routine. This followup sets the default higher up the stack within
AddReturn which provider clearer logic and a small performance
improvment.

Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>

Signed-off-by: Josef Moravec <josef.moravec@gmail.com>

Signed-off-by: Nick Clemens <nick@bywatersolutions.com>