When destroying a block job in block_job_unref() we should remove it
from the job list before calling block_job_remove_all_bdrv().

This is because removing the BDSs can trigger an aio_poll() and wake
up other jobs that might attempt to use the block job list. If that
happens the job we're currently destroying should not be in that list
anymore.

Signed-off-by: Alberto Garcia <berto@igalia.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>