fixed possible crash if nlriToIPNet result is null
fixed possible crash if nlriToIPNet result is null

a16/gobgp,osrg/gobgp,a16/gobgp,fujita/gobgp,fujita/gobgp,fujita/gobgp,fujita/gobgp,a16/gobgp,osrg/gobgp,a16/gobgp,a16/gobgp,osrg/gobgp,a16/gobgp,osrg/gobgp,a16/gobgp