[gnome-db] Problems with mainpagetable.c

[Vivien Malerba <malerba gnome-db org>]

Hi!

I've noticed than there are some problems with the MainPageTable widget
when the connection is closed. BTW, I really like the GnomeDbGrid widget and its
data model.

I've updated a bit the code because normally every row in the model has
a Row_Data pointer which must not be null. I think there is a problem
somewhere, maybe in the GdaDataModel code because if you uncomment line
591 then when the next table is removed, the assertion line 588 will not
be true whereas it should be.

Thanks,

Vivien