Bug 19033: XSS Flaws in Currencies and exchange page

Bug 19033: XSS Flaws in Currencies and exchange page

1. Hit /cgi-bin/koha/admin/currency.pl
2. Enter <IFRAME SRC="javascript:alert('XSS');"></IFRAME> search currencies box.
3. Notice the iframe is executed
4. Apply patch
5. Reload page, and enter iframe again on search currencies box.
6. Notice it is no longer executed

Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
Fixes the issue, follows common practice on the codebase.

Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>