udevd: detach event from worker if we kill a worker

Jul  8 09:36:41 udevd[663]: worker [5491] did not accept message, kill it
Jul  8 09:36:41 udevd[663]: worker [5491] unexpectedly returned with 0
Jul  8 09:36:41 udevd[663]: worker [5551] unexpectedly returned with 0
Jul  8 09:36:41 kernel: [  156.832086] <6>udevd[663]: segfault at 4 ip 00959fbc sp bfbe7b78 error 6 in udevd[94f000+1c000]

https://bugs.launchpad.net/ubuntu/+source/udev/+bug/396957