fix[fuzz]: scalar_at baseline handle nulls (#5150)

Signed-off-by: Joe Isaacs <[email protected]>

Author: joseph-isaacs

fuzz/src/array/scalar_at.rs

@@ -13,6 +13,9 @@ use vortex_scalar::{DecimalValue, Scalar, match_each_decimal_value_type};
 /// This implementation manually extracts the scalar value from each canonical type
 /// without using the scalar_at method, to serve as an independent baseline for testing.
 pub fn scalar_at_canonical_array(canonical: Canonical, index: usize) -> VortexResult<Scalar> {
+    if canonical.as_ref().is_invalid(index) {
+        return Ok(Scalar::null(canonical.as_ref().dtype().clone()));
+    }
     Ok(match canonical {
         Canonical::Null(_array) => Scalar::null(DType::Null),
         Canonical::Bool(array) => {