rows.Close() must not overwrite buffer

[methane]

Read these:

• golang/go@651ddbd
• database/sql: QueryContext() and Scan() data race golang/go#23519

From Go 1.10, it's not allowed anymore. Maybe, it should be avoided from Go 1.9.
We should use another buffer...

This issue caused #902.

[DoctorQ]

my problem is caused by this？

[methane]

Yes, but please don't reply here. I create this issue instead of reopen #902 because I want to focus important design topic.

[methane]

I think avoiding one allocation for each query is too difficult.

[vmg]

I've implemented a potential fix in #943 and discussed several other approaches which I believe are inferior to the one I'm proposing. Feedback is welcome.

[methane]

I created reproducer: https://gist.github.com/methane/418f872d788209116f8a5d08f756d838
go run -race reports race too.

To reproduce, we need to use sql.RawBytes or some Scanner object which doesn't deep copy []byte.