Bad default of 1 in XWiki.isMultilingual instead of 0 (when no XWikiPreferences object exists)

When, for instance, the Distribution Wizard is started on first boot of a XEM instance, if a cookie exists stating that the language is fr, the DW will read and use it instead of defaulting to English.

This happens because XWiki.isMultilingual(...) returns true (by default) instead of false.

The default value in XWikiPreferences is set to false, so, XWiki.isMultilingual(...) should do the same.