sesutil: fix Coverity CIDs

• 1411604: file descriptor leak
• 1411586: memory leaks, null dereference on ENOMEM

Reported by: Coverity Scan
Coverity CIDs: 1411604, 1411586
Reviewed by: trasz
MFC after: 2 weeks
Sponsored by: Axcient
Differential Revision: https://reviews.freebsd.org/D23651