Since we do free subtopic and desc in help_getnext(), we need to set them also
NULL, so we make sure we dont get double free().
Approved by: bapt
Differential Revision: https://reviews.freebsd.org/D15082
With r328289 we attempt to make sure we free the resources allocated in
help_getnext(), however, it is possible that we get no resources allocated
and help_getnext() will return early.
Make sure we have pointers set to NULL early in help_getnext().
Reported by: Andy Fiddaman
Right now, we'll leak memory when we display a help topic because we
don't free t, s, d that we've just used when breaking out of the loop.
NB: coverity just reported t, but s and d also leak.
CID: 1007776
