Bug 16035: MARC default bibliographic framework Export fix

Bug 16035: MARC default bibliographic framework Export fix

This patch makes sure that, if there is no framework code,
     $frameworkcode is set to 'default'. This fixes the format issue.
     Then, if $frameworkcode = default, an empty string (rather than
     null) is passed to the ExportFramework method, as the framework
     code in the DB for default codes is "".

To test:
1) Go to Admin -> MARC Bibliographic framework
2) Try to export default framework in all formats, notice the file is
only exported as .ods and is an empty file. Notice warns in intranet
error log.
3) Apply patch and refresh page
4) Confirm exporting default framework works in all formats and
spreadsheet has data
5) Notice warns in error log are gone
6) Confirm export still works for other frameworks

Sponsored-by: Catalyst IT
Signed-off-by: Owen Leonard <oleonard@myacpl.org>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
(cherry picked from commit 705097f938ba9334c21b3e6f006bd7c9ba38763c)
Signed-off-by: Frédéric Demians <f.demians@tamil.fr>
(cherry picked from commit 1de610bb63f70b9f4a1e3a8a5683de5d3bb7bb12)
Signed-off-by: Julian Maurice <koha@matrix-jessie>