Fix zone2{sql,json} exit codes

To be consistent with general practice, fix zone2{sql,json} to exit
with:
 * 0 on success
 * 1 on error

This also moves the catch block after the last line of main, so a
"theoretically" possible exception in ::arg().mustDo would get caught.
(Also, one level less of indent!)
Merge pull request #979 from zeha/zone2xxx-exit-codes

Fix zone2{sql,json} exit codes