Prevent panics

Signed-off-by: Oliver Tale-Yazdi <oliver.tale-yazdi@parity.io>

primitives/arithmetic/src/per_things.rs

@@ -479,6 +479,10 @@ where
 	P::Inner: Into<N>,
 {
 	let maximum: N = P::ACCURACY.into();
+	if part.is_zero() {
+		// Division by zero... best effort to prevent a panic.
+		return maximum
+	}
 	let c = rational_mul_correction::<N, P>(x.clone(), P::ACCURACY, part, rounding);
 	(x / part.into()).saturating_mul(maximum).saturating_add(c)
 }
@@ -509,6 +513,10 @@ where
 	let numer_upper = P::Upper::from(numer);
 	let denom_n: N = denom.into();
 	let denom_upper = P::Upper::from(denom);
+	if denom.is_zero() {
+		// Division by zero... best effort to prevent a panic.
+		return N::one()
+	}
 	let rem = x.rem(denom_n);
 	// `rem` is less than `denom`, which fits in `P::Inner`.
 	let rem_inner = rem.saturated_into::<P::Inner>();