fix: PLONK verifier gadget in-circuit without commitments

[ivokub]

From #949.

The issue is that if we do not use commitments then verification key points may be zero. But for perf we use unsafe operations.

I would still like to get PLONK verification without commitment working. I'm actually thinking about adding new algopt option algopts.ForceSafe which performs safe arithmetic inside MSM. It is suboptimal (we could also only omit the selector we know is 0), but atleast would cover different cases. And I think we already know inside the circuit if there is commitment or not.