Bug 17206: Fix switch to default framework

Bug 17206: Fix switch to default framework

When editing a bibliographic record, if you switch the framework to
default, the page is reloaded but the framework is not changed.
From the pl script, you can see that the frameworkcode is set to the one
of the biblio if set to false. The empty string, which means default,
should be taken into account.

Test plan:
- Create a record using the Fast add framework
- Save the record
- Open the record for editing
- Use the "Settings" pull down to change the framework to default
- Try another framework
- Try changing to default from there

Signed-off-by: Owen Leonard <oleonard@myacpl.org>
Signed-off-by: Katrin Fischer  <katrin.fischer@bsz-bw.de>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
(cherry picked from commit bd0d1dd6b1eeb51540a6121c8ed84330e5f48eff)
Signed-off-by: Frédéric Demians <f.demians@tamil.fr>