Fix out of bounds when verifying malformed proofs

Author: Daniel Kuehr

poly-commitment/src/commitment.rs

@@ -738,6 +738,13 @@ impl<G: CommitmentCurve> SRS<G> {
             };
 
             let s = b_poly_coefficients(&chal);
+            
+            debug_assert!(s.len() <= scalars.len());
+
+            // TODO: implement a better solution at type/wire level, for now we just bail out...
+            if s.len() > scalars.len() {
+                return false;
+            }
 
             let neg_rand_base_i = -rand_base_i;