Add test for empty matrix multiplication.

tests/core/empty.rs

@@ -0,0 +1,9 @@
+use na::{DMatrix, DVector};
+
+#[test]
+fn empty_mul() {
+    // Issue #644
+    let m = DMatrix::<f32>::zeros(8, 0);
+    let v = DVector::<f32>::zeros(0);
+    assert_eq!(m * v, DVector::zeros(8));
+}

tests/core/mod.rs

@@ -8,6 +8,7 @@ mod matrix_slice;
 #[cfg(feature = "mint")]
 mod mint;
 mod serde;
+mod empty;
 
 
 #[cfg(feature = "arbitrary")]