Fix zero handling in AxisChunksIter/Mut

Now, chunk size of zero and axis length of zero are handled correctly.

Author: jturner314

src/impl_methods.rs

@@ -1005,7 +1005,7 @@ where
     /// The last view may have less elements if `size` does not divide
     /// the axis' dimension.
     ///
-    /// **Panics** if `axis` is out of bounds.
+    /// **Panics** if `axis` is out of bounds or if `size` is zero.
     ///
     /// ```
     /// use ndarray::Array;
@@ -1036,7 +1036,7 @@ where
     ///
     /// Iterator element is `ArrayViewMut<A, D>`
     ///
-    /// **Panics** if `axis` is out of bounds.
+    /// **Panics** if `axis` is out of bounds or if `size` is zero.
     pub fn axis_chunks_iter_mut(&mut self, axis: Axis, size: usize) -> AxisChunksIterMut<A, D>
     where
         S: DataMut,

src/iterators/mod.rs

@@ -1206,21 +1206,28 @@ clone_bounds!(
 ///
 /// Returns an axis iterator with the correct stride to move between chunks,
 /// the number of chunks, and the shape of the last chunk.
+///
+/// **Panics** if `size == 0`.
 fn chunk_iter_parts<A, D: Dimension>(
     v: ArrayView<A, D>,
     axis: Axis,
     size: usize,
 ) -> (AxisIterCore<A, D>, usize, D) {
+    assert_ne!(size, 0, "Chunk size must be nonzero.");
     let axis_len = v.len_of(axis);
-    let size = if size > axis_len { axis_len } else { size };
     let n_whole_chunks = axis_len / size;
     let chunk_remainder = axis_len % size;
     let iter_len = if chunk_remainder == 0 {
         n_whole_chunks
     } else {
         n_whole_chunks + 1
     };
-    let stride = v.stride_of(axis) * size as isize;
+    let stride = if n_whole_chunks == 0 {
+        // This case avoids potential overflow when `size > axis_len`.
+        0
+    } else {
+        v.stride_of(axis) * size as isize
+    };
 
     let axis = axis.index();
     let mut inner_dim = v.dim.clone();