fix: avoid malicious hint in BN254 final exp check

[yelhousni]

Description

Fixes #1213

Type of change

• Bug fix (non-breaking change which fixes an issue)

How has this been tested?

Same tests.

How has this been benchmarked?

no change.

Checklist:

• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works
• I did not modify files generated from templates
• golangci-lint does not output errors locally
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules

[ivokub]

LGTM

[ivokub]

I think it is sufficient that the hint returns error when previous Miller Loop result is zero. Imo it cannot really happen in any valid cases and would probably mean that the input wasn't previous Miller loop result or the accumulator was not correctly initialized.