add missing error checks in simple example

[stanim]

Any error encountered during iteration should be handled properly, see:
https://golang.org/pkg/database/sql/#Rows
http://go-database-sql.org/retrieving.html

[coveralls]

Coverage remained the same at 68.137% when pulling ed21175 on stanim:errs into 37aa7c6 on mattn:master.

[mattn]

thank you

[stanim]

You're welcome.