Bug 8947: [SIGNED-OFF] XSLT fallback logic backwards

Bug 8947: [SIGNED-OFF] XSLT fallback logic backwards

The logic for the XSLT fallback was backwards, which meant that
non-English installations of the CCSR theme were unable to use XSLT
stylesheets. This patch corrects the logic.

To test:
1) Switch to the ccsr OPAC theme.
2) Switch to a language other than English for the OPAC.
3) Turn on the default XSLT stylesheets for the OPAC.
4) Do a search or view a record that would result in something being
   displayed with XSLT. This will work after the patch, but not before.

Signed-off-by: Magnus Enger <magnus@enger.priv.no>
Works as advertised!

Signed-off-by: Paul Poulain <paul.poulain@biblibre.com>