s3/utils: Fix double free error with smbtree

s3/utils: Fix double free error with smbtree

==3632==
WORKGROUP
	\\ATP
		\\ATP\IPC$           	IPC Service ()
==3632== Invalid read of size 8
==3632==    at 0x773C926: poptResetContext (in /usr/lib64/libpopt.so.0.0.0)
==3632==    by 0x773E5DD: poptFreeContext (in /usr/lib64/libpopt.so.0.0.0)
==3632==    by 0x10A8BC: main (smbtree.c:354)
==3632==  Address 0x16085e00 is 640 bytes inside a block of size 784 free'd
==3632==    at 0x4C2F1AD: free (vg_replace_malloc.c:530)
==3632==    by 0x773E6F7: poptFreeContext (in /usr/lib64/libpopt.so.0.0.0)
==3632==    by 0x10A84B: main (smbtree.c:342)
==3632==  Block was alloc'd at
==3632==    at 0x4C2FE45: calloc (vg_replace_malloc.c:711)
==3632==    by 0x773C79A: poptGetContext (in /usr/lib64/libpopt.so.0.0.0)
==3632==    by 0x10A829: main (smbtree.c:339)
==3632==

BUG: https://bugzilla.samba.org/show_bug.cgi?id=14332
Signed-off-by: Noel Power <npower@samba.org>
Reviewed-by: Volker Lendecke <vl@samba.org>
Autobuild-User(master): Noel Power <npower@samba.org>
Autobuild-Date(master): Wed Apr  1 18:51:43 UTC 2020 on sn-devel-184

(cherry picked from commit 24b03fd28ed19cea8f875f96b3e300f808dfc4ae)

Autobuild-User(v4-12-test): Karolin Seeger <kseeger@samba.org>
Autobuild-Date(v4-12-test): Fri Apr  3 12:24:36 UTC 2020 on sn-devel-184