dbcon: fix a bug with the SQL generation of the union function.
dbcon: fix a bug with the SQL generation of the union function.

The join wasn't being cleared after the union, now it is.

tardypad/lunr,tardypad/lunr,pprkut/lunr,tardypad/lunr,M2Mobi/lunr,pprkut/lunr,M2Mobi/lunr,pprkut/lunr,M2Mobi/lunr