npe fix

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@36917 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e
#4638 fix - reloading preferences on file->new

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@36918 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e