Fix multiplication between matrices of dimension 0.

Fix #644

src/base/blas.rs

@@ -565,6 +565,7 @@ where
         );
 
         if ncols2 == 0 {
+            self.fill(N::zero());
             return;
         }
 
@@ -1006,6 +1007,12 @@ where N: Scalar + Zero + ClosedAdd + ClosedMul
                 "gemm: dimensions mismatch for addition."
             );
 
+
+            if a.ncols() == 0 {
+                self.fill(N::zero());
+                return;
+            }
+
             // We assume large matrices will be Dynamic but small matrices static.
             // We could use matrixmultiply for large statically-sized matrices but the performance
             // threshold to activate it would be different from SMALL_DIM because our code optimizes