Add unit test case to improve test coverage for go/sqltypes/named_result.go
Add unit test case to improve test coverage for go/sqltypes/named_result.go

Signed-off-by: Hu Shuai <a4797ccdc3c71d8ffc5c17a5bb7f114e3818f278@cn.fujitsu.com>

vitessio/vitess,tinyspeck/vitess,mahak/vitess,vitessio/vitess,vitessio/vitess,mahak/vitess,tinyspeck/vitess,tinyspeck/vitess,mahak/vitess,vitessio/vitess,mahak/vitess,mahak/vitess,vitessio/vitess,tinyspeck/vitess,vitessio/vitess,vitessio/vitess,vitessio/vitess,tinyspeck/vitess,mahak/vitess,tinyspeck/vitess,mahak/vitess,tinyspeck/vitess,mahak/vitess