fix test code for mrn_rnd_next.
fix test code for mrn_rnd_next.

mroonga/mroonga,mroonga/mroonga,naoa/mroonga,naoa/mroonga,yoku0825/mroonga,mroonga/mroonga,yoku0825/mroonga,yoku0825/mroonga,naoa/mroonga,yoku0825/mroonga,yoku0825/mroonga,mroonga/mroonga,naoa/mroonga,yoku0825/mroonga,naoa/mroonga,naoa/mroonga