solver: stub out sysSampler close

[jedevc]

Fixes #4774.

Follow-up to #4040 (cc @thaJeztah) - this didn't resolve the access to sysSampler.Close, we need to stub this one out as well!

[thaJeztah]

Changes SGTM, but also wondering; now that Windows is becoming an actual thing; should we consider newSysSampler() to return an actual sysSampler (with stubs for its methods)?

My slight concern here is that this will bring us down the road of other code hiding potential issues (if it's nil).

[jedevc]

Changes SGTM, but also wondering; now that Windows is becoming an actual thing; should we consider newSysSampler() to return an actual sysSampler (with stubs for its methods)?

My slight concern here is that this will bring us down the road of other code hiding potential issues (if it's nil).

Sure, no reason to not do this IMO - we could have a dummySysSampler. That said, this is a super easy to cherry-pick change, and it's easy to manually verify that we've now got all the access points to this private field.

[thaJeztah]

Yes, I guess for cherry-picking this one is fine to fix the immediate issue at hand.

[thaJeztah]

LGTM for the immediate issue (but not a maintainer)