Bug 8646 - prevent the highlighter from going infinite loop

Bug 8646 - prevent the highlighter from going infinite loop

On certain search queries, for example
http://koha-intra/cgi-bin/koha/catalogue/search.pl?kw=idx&q=ti:book%20
the highlighter starts going into an infinite loop until the browser
decides to kill it.

This patch prevents the bad input going to the highlighter.

It also includes the fix on the OPAC, even though the issue doesn't come
up there. Better to be safe...

Signed-off-by: Jonathan Druart <jonathan.druart@biblibre.com>
Signed-off-by: Paul Poulain <paul.poulain@biblibre.com>
Signed-off-by: Chris Cormack <chrisc@catalyst.net.nz>