message: Fix matrix product with zero rows
  Fixes
diff: @@ -229,7 +229,7 @@ where
  assert_eq!(l_cols, r_rows);
  let workspace_len = l_rows.max(l_cols).max(r_cols);
  #[cfg(feature = "multi_thread")]
  - let nb_threads = std::cmp::min(l_rows, {
  + let nb_threads = std::cmp::min(l_rows.max(1), {
  use self::ThreadingStrategy::{Automatic, AutomaticPhysical};
  match thread_threading_strategy() {
  ThreadingStrategy::Fixed(nb_threads) => nb_threads,
  @@ -509,6 +509,22 @@ mod test {
  assert_eq!(exp, res);
  }
  + #[test]
  + fn mul_zero_rows() {
  + // See https://github.com/vbarrielle/sprs/issues/239
  + let a = crate::CsMat::new((0, 11), vec![0], vec![], vec![]);
  + let b = crate::CsMat::new(
  + (11, 11),
  + vec![0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
  + vec![],
  + vec![],
  + );
  + let c: crate::CsMat<f64> = &a * &b;
  + assert_eq!(c.rows(), 0);
  + assert_eq!(c.cols(), 11);
  + assert_eq!(c.nnz(), 0);
  + }
  +
  #[test]
  #[cfg(feature = "multi_thread")]
  fn mul_csr_csr_multithreaded() {
  