Bug 21703: Fix filter on dataurl variable to allow placing holds in staff again

Bug 21703: Fix filter on dataurl variable to allow placing holds in staff again

We must not encode & again and use the url filter, instead of uri.

To test:
- Search for a record in staff
- Go to holds
- Search for patrons, multiple should be displayed
- Pick a patron by clicking on the name
- Verify an error is shown and the URL is incorrect
- Apply patch
- Repeat test above, placing a hold should now work.

Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>