blockjobs: fix set-speed kick

If speed is '0' it's not actually "less than" the previous speed.
Kick the job in this case too.

Signed-off-by: John Snow <jsnow@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
1 file changed