Bug 37965: (QA follow-up) fix WYSIWYG in sysprefs

Bug 37965: (QA follow-up) fix WYSIWYG in sysprefs

Test plan:
1. Go to http://localhost:8081/cgi-bin/koha/admin/preferences.pl?
op=search&searchfield=UseWYSIWYGinSystemPreferences
2. Enable the system preference to show WYSIWYG in HTML system preferences
3. Go to http://localhost:8081/cgi-bin/koha/admin/preferences.pl?
op=search&searchfield=OPACSearchForTitleIn
4. Add a link for "http://localhost:8081/cool.pl"
5. Note in the source code that the URL gets mangled

6. Apply the patch

7. Repeat the above test plan
8. Note that the URL has NOT been mangled and remains
http://localhost:8081/cool.pl

Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>