Return ExecutedQueryString even when an error is returned

[gabor]

currently, when there's an error (for example an error in the sql query), we do not get back the executed-query-string into grafana's query inspector:

• in QueryDB we do construct a dataframe with the required metadata: https://github.com/grafana/sqlds/blob/3c409475badfb0bad9e76f547fa01a676d351e0a/query.go#L64
• but in handleQuery, when QueryDB ends with an error, we do not return the "returned" dataframe in the general case: https://github.com/grafana/sqlds/blob/3c409475badfb0bad9e76f547fa01a676d351e0a/datasource.go#L294

this PR returns the result, but i'm not sure if this is the best approach. could there be some leak of info with this that we want to avoid? WDYT?

[CLAassistant]

All committers have signed the CLA.

[scottlepp]

I think it's just confusion with the sdk that you can return a frame with an error, and an error. And when should a frame be returned with an error vs an error. And if a frame is returned with an error, do we also return an error.

EDIT: I see the explanation here.

[gabor]

to be honest, when i write go, i prefer the pattern that if err == nil, then i ignore the result...but that would complicate the code a bit too much.