fix(falcon): add missing return in Polynomial::div for zero numerator

[Sertug17]

Summary

Fixes 0xMiden/miden-vm#3534

Polynomial::div discards the result of Self::zero() when the numerator is zero because the return keyword is missing. Execution falls through to the division loop where remainder.degree().unwrap() panics on None.

Fix

// Before (bug)
if self.is_zero() {
    Self::zero();  // result discarded, no return
}

// After
if self.is_zero() {
    return Self::zero();
}

Testing

Dividing a zero polynomial by a non-zero polynomial now returns zero instead of panicking.

[github-actions]

Automated check (CONTRIBUTING.md)

Findings:

• Ensure issue bug: missing return in Polynomial::div causes panic on zero numerator miden-vm#3534 is assigned to the PR author.

Recommendations:

• Consider adding a Test plan or clear review steps.

Next steps:

• Ensure issue bug: missing return in Polynomial::div causes panic on zero numerator miden-vm#3534 is assigned to you.
• See CONTRIBUTING.md for expectations.
• If this is a false positive, comment: /quality-review.

[Sertug17]

/quality-review

The automated check flagged this as trivial. I'll add a regression test for zero numerator division. Pushing shortly.

[Sertug17]

/quality-review

Added a regression test (div_zero_numerator_returns_zero) that verifies zero divided by non-zero returns zero instead of panicking. Force-pushed.