qemu_migration: Avoid writing to freed memory

qemu_migration: Avoid writing to freed memory

When a domain is killed on the source host while it is being migrated
and libvirtd is waiting for the migration to finish (waiting for the
domain condition in qemuMigrationSrcWaitForCompletion), the run-time
state including priv->job.current may already be freed once
virDomainObjWait returns with -1. Thus the priv->job.current pointer
cached in jobInfo is no longer valid and setting jobInfo->status may
crash the daemon.

https://bugzilla.redhat.com/show_bug.cgi?id=1593137

Signed-off-by: Jiri Denemark <jdenemar@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>