fix small error

crates/polars-core/src/chunked_array/ops/zip.rs

@@ -1,3 +1,5 @@
+use std::borrow::Cow;
+
 use arrow::bitmap::Bitmap;
 use arrow::compute::utils::{combine_validities_and, combine_validities_and_not};
 use polars_compute::if_then_else::{if_then_else_validity, IfThenElseKernel};
@@ -231,7 +233,9 @@ impl ChunkZip<StructType> for StructChunked {
         // - Each chunkedarray has an equal length (i.e. is broadcasted)
         //
         // Therefore, we broadcast only those that are necessary to be broadcasted.
-        let needs_broadcast = if_true.chunks() > 1 || if_false.chunks() > 1 || mask.chunks() > 1;
+        let needs_broadcast = if_true.chunks().len() > 1
+            || if_false.n_chunks().len() > 1
+            || mask.n_chunks().len() > 1;
         if needs_broadcast && length > 1 {
             // Special case. In this case, we know what to do.
             if mask.length == 1 {