- fix compiler warning and bug in new isolate() command
- fix compiler warning and bug in new isolate() command

(sorry Milena, I had not detected this despite compiling&testing because
 I configure with --disable-optimize such that I compile with just -g and
 not -g -O2; in which case the warning is not given)

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