s3:auth:check_sam_security: null out sampass after it has been stolen.

s3:auth:check_sam_security: null out sampass after it has been stolen.

So that a later talloc_free would not harm. I could have used
talloc_move instead of talloc steal in make_server_info_sam(),
but this would have required a change of the signature.

Michael
(cherry picked from commit 1bb4a2ca3a1e11b395b3b819e468ecac67e16d64)