monetdbd: fix setting of default dbfarm string
monetdbd: fix setting of default dbfarm string

Regression introduced at alloca removal.  Make sure we always set dbfarm
to it default, such that we also have it set when there are no arguments
provided to monetdbd.  This makes a simple 'monetdbd' start again,
instead of reporting on some garbage string not existing.

zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb