Bug 11986: fix searching by tags in OPAC when DOM mode is in use

This patch fixes the following issue: in installations that are using
zebra DOM indexing for bibliographic records, tag searching in OPAC
doesn't work properly (clicking on any tag in OPAC leads to "404 error").

To test: ensure that with patch applied:
1) problems with tag searching get resolved for [some] test
configuration with biblio DOM indexing enabled,
2) there are no apparent tag-searching-related regressions in OPAC,
in some yet another test installation configured with legacy
(grs1) indexing mode for biblios.

Signed-off-by: Chris Cormack <chris@bigballofwax.co.nz>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Galen Charlton <gmc@esilibrary.com>