Bug 27645: Prevent "is on hold" warning to be displayed twice

Bug 27645: Prevent "is on hold" warning to be displayed twice

During a batch checkout we display the "item is on hold" message
depending on different conditions.
However it can happen the message is displayed twice.

If the checkout is not impossible then we see:
This item is on hold for another patron.
This item is on hold for another patron. The hold will be overridden, but not cancelled.

We should only display the second one.

Test plan:
With a default ktd setup you can simply place an item on hold and use the
batch checkout tool to check it out

Signed-off-by: Lucas Gass <lucas@bywatersolutions.com>
Signed-off-by: Julian Maurice <julian.maurice@biblibre.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>