Don't modify nil getnetworkinfo result.

Since the result might not be set when the response does not contain one,
such as in the case when the command is not implemented by the server,
don't attempt to modify it until ensuring it exists.

jsonresults.go

@@ -580,7 +580,7 @@ func ReadResultCmd(cmd string, message []byte) (Reply, error) {
 		var res *GetNetworkInfoResult
 		err = json.Unmarshal(objmap["result"], &res)
 		if err == nil {
-			if res.LocalAddresses == nil {
+			if res != nil && res.LocalAddresses == nil {
 				res.LocalAddresses = []LocalAddressesResult{}
 			}
 			result.Result = res