Previewing a new document cause XWD_TRANSLATION to be set

This issue create corrupted records in xwikidoc table that could be found using the following request:

select XWD_FULLNAME, XWD_DEFAULT_LANGUAGE, XWD_LANGUAGE, XWD_TRANSLATION from xwikidoc where (XWD_LANGUAGE = "" OR (XWD_LANGUAGE IS NULL and "" IS NULL)) and XWD_TRANSLATION != 0

I have attached a very careful patch (not so beautiful since the whole stuff is badly designed) that shoud avoid this issue. To fix older records, a database migration code should be written to execute in HQL the equivalent of:

update xwikidoc set XWD_TRANSLATION=0 where (XWD_LANGUAGE = "" OR (XWD_LANGUAGE IS NULL and "" IS NULL)) and XWD_TRANSLATION != 0;

I let you wrote it, since I am not well aware of the database migration procedures.