Bug 28475: Fix searching all headings

Bug 28475: Fix searching all headings

This patch fixes the value of a hidden input that was mistakenly
changed and prevents search all headings from working.

To test:
1. Open the authorities section in the OPAC
2. Choose the 'Search all headings' tab
3. Search for 'a'
=> FAIL: No results
4. Empty the search box, and make sure 'Search all headings' is selected
=> SUCCESS: There are authority records
5. Apply this patch
6. Reload the page
7. Retry 3 and 4
=> SUCCESS: Searching is back!
8. Sign off :-D

Sponsored-by: Asociación Latinoamericana de Integración
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
Signed-off-by: Victor Grousset/tuxayo <victor@tuxayo.net>
Signed-off-by: Lucas Gass <lucas@bywatersolutions.com>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>