Bug 26249: Set keep_text class correctly in cat-search.inc

Bug 26249: Set keep_text class correctly in cat-search.inc

This patch sets the keep_text class correctly in cat-search.inc
for the "Search the catalog" tab

To test:
1) Apply the patch
2) Go to /cgi-bin/koha/catalogue/search.pl
3) Type "A" into the search box for "Search the catalog"
4) Click on the "Check out" tab
5) Note that "A" appears in search box
6) Change "A" to "B" in search box
7) Click on the "Search the catalog" box
8) Note that "B" appears in the search box
9) Note no Javascript errors in the console

Signed-off-by: Didier Gautheron <didier.gautheron@biblibre.com>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>