free and clear the gl_pathv pointer in the glob_t structure. Such
breaks the invariant of the glob_t structure, as stated in the comment
right in front of the globextend() function. If gl_pathv was non-NULL,
then gl_pathc was > 0. Making gl_pathv a NULL pointer without also
setting gl_pathc to 0 is wrong.
Since we otherwise don't free the memory associated with a glob_t in
error cases, it's unlikely that this change will cause a memory leak
that wasn't already there to begin with. Callers of glob(3) must
call globfree(3) irrespective of whether glob(3) returned an error
or not.