Bug 21151: Fix SRU search fields mapping pop-up

Bug 21151: Fix SRU search fields mapping pop-up

The SRU search fields mapping pop-up comes up as a blank white
page.

To test:
- Go to Administration > Z39.50/SRU servers
- Modify or create an SRU server
- Click on the 'Modify' button to change mappings
- Verify the new window that opens is blank
- Apply patch
- Verify the pop-up now is no longer blank but works
  correctly.

Bonus: Spottd some HTML errors while looking for the
       problem. Also fixed in the patch.

Signed-off-by: Owen Leonard <oleonard@myacpl.org>
Signed-off-by: Julian Maurice <julian.maurice@biblibre.com>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>