Fix for the omprog module -- calling execve() with a NULL second
argument doesn't work. Instead supply an argv list with just a
terminating NULL entry.

Submitted upstream as https://github.com/rsyslog/rsyslog/pull/1618

Patch files regenerated by 'make makepatch'

Reported by: (Chun-Tien Chang) <tcs@kitty.2y.idv.tw>