Fix cli crash when showing neighbor stats as list.
Fix cli crash when showing neighbor stats as list.

If the gRPC-server has TLS enabled, but the cli is used without TLS,
it crashes when listing neighbors with a segfault due to an unhandled
error.

fujita/gobgp,osrg/gobgp,fujita/gobgp,tamihiro/gobgp,fujita/gobgp,a16/gobgp,a16/gobgp,j-kato/gobgp,tamihiro/gobgp,a16/gobgp,tamihiro/gobgp,a16/gobgp,a16/gobgp,a16/gobgp,osrg/gobgp,fujita/gobgp,a16/gobgp,osrg/gobgp,j-kato/gobgp,tamihiro/gobgp,j-kato/gobgp,osrg/gobgp