[bugfix] fix NPE in XSLTServlet if stylesheet could not be found in db.
[bugfix] fix NPE in XSLTServlet if stylesheet could not be found in db.

svn path=/trunk/eXist/; revision=10962

RemiKoutcherawy/exist,jensopetersen/exist,zwobit/exist,eXist-db/exist,hungerburg/exist,lcahlander/exist,ljo/exist,windauer/exist,jensopetersen/exist,kohsah/exist,RemiKoutcherawy/exist,windauer/exist,dizzzz/exist,opax/exist,shabanovd/exist,wshager/exist,wshager/exist,RemiKoutcherawy/exist,patczar/exist,wshager/exist,MjAbuz/exist,kohsah/exist,jessealama/exist,patczar/exist,wolfgangmm/exist,lcahlander/exist,wshager/exist,zwobit/exist,dizzzz/exist,dizzzz/exist,olvidalo/exist,shabanovd/exist,windauer/exist,jessealama/exist,lcahlander/exist,patczar/exist,eXist-db/exist,ambs/exist,wolfgangmm/exist,dizzzz/exist,ambs/exist,shabanovd/exist,zwobit/exist,ambs/exist,ljo/exist,eXist-db/exist,lcahlander/exist,opax/exist,ambs/exist,opax/exist,jensopetersen/exist,jensopetersen/exist,jessealama/exist,eXist-db/exist,jensopetersen/exist,ambs/exist,RemiKoutcherawy/exist,shabanovd/exist,zwobit/exist,lcahlander/exist,jessealama/exist,patczar/exist,eXist-db/exist,wolfgangmm/exist,kohsah/exist,windauer/exist,RemiKoutcherawy/exist,ljo/exist,jessealama/exist,kohsah/exist,jessealama/exist,hungerburg/exist,ambs/exist,MjAbuz/exist,patczar/exist,adamretter/exist,olvidalo/exist,joewiz/exist,jensopetersen/exist,wolfgangmm/exist,hungerburg/exist,joewiz/exist,RemiKoutcherawy/exist,joewiz/exist,ljo/exist,olvidalo/exist,MjAbuz/exist,dizzzz/exist,adamretter/exist,ljo/exist,hungerburg/exist,shabanovd/exist,hungerburg/exist,windauer/exist,lcahlander/exist,joewiz/exist,opax/exist,adamretter/exist,MjAbuz/exist,wolfgangmm/exist,adamretter/exist,ljo/exist,adamretter/exist,joewiz/exist,eXist-db/exist,kohsah/exist,shabanovd/exist,zwobit/exist,olvidalo/exist,MjAbuz/exist,wshager/exist,patczar/exist,wolfgangmm/exist,wshager/exist,opax/exist,zwobit/exist,adamretter/exist,olvidalo/exist,windauer/exist,kohsah/exist,MjAbuz/exist,dizzzz/exist,joewiz/exist