aio_aqueue(): avoid ucred leak on failure path
Approved by: so
Security: FreeBSD-SA-22:10.aio
PR: 258698
Submitted by: sigsys@gmail.com
(cherry picked from commit 45c2c7c484de7747014492b17ff89e323ee66496)
(cherry picked from commit 76ed54dda74ffe8c7284cab10a4b30445a8db12f)