s3-utils: fix format-truncation in smbpasswd

s3-utils: fix format-truncation in smbpasswd

../source3/utils/smbpasswd.c: In function ‘process_root’:
../source3/utils/smbpasswd.c:414:37: error: ‘$’ directive output may be truncated writing 1 byte into a region of size between 0 and 255 [-Werror=format-truncation=]
   slprintf(buf, sizeof(buf) - 1, "%s$", user_name);
                                     ^
In file included from ../source3/include/includes.h:23,
                 from ../source3/utils/smbpasswd.c:19:
../lib/replace/../replace/replace.h:514:18: note: ‘snprintf’ output between 2 and 257 bytes into a destination of size 255
 #define slprintf snprintf
../source3/utils/smbpasswd.c:414:3: note: in expansion of macro ‘slprintf’
   slprintf(buf, sizeof(buf) - 1, "%s$", user_name);
   ^~~~~~~~
../source3/utils/smbpasswd.c:397:35: error: ‘$’ directive output may be truncated writing 1 byte into a region of size between 0 and 255 [-Werror=format-truncation=]
   slprintf(buf, sizeof(buf)-1, "%s$", user_name);
                                   ^
In file included from ../source3/include/includes.h:23,
                 from ../source3/utils/smbpasswd.c:19:
../lib/replace/../replace/replace.h:514:18: note: ‘snprintf’ output between 2 and 257 bytes into a destination of size 255
 #define slprintf snprintf
../source3/utils/smbpasswd.c:397:3: note: in expansion of macro ‘slprintf’
   slprintf(buf, sizeof(buf)-1, "%s$", user_name);
   ^~~~~~~~
cc1: some warnings being treated as errors

BUG: https://bugzilla.samba.org/show_bug.cgi?id=13437

Pair-Programmed-With: Andreas Schneider <asn@samba.org>

Signed-off-by: Guenther Deschner <gd@samba.org>
Signed-off-by: Andreas Schneider <asn@samba.org>
(cherry picked from commit 9b6dc8f504c406ed8a044e5becca7e8f01da6c84)