Fixed commainitializer test.

The removed `finished()` call was responsible for enforcing that the
initializer was provided the correct number of values. Putting it back in
to restore previous behavior.

Eigen/src/Core/CommaInitializer.h

@@ -107,6 +107,7 @@ struct CommaInitializer
   EIGEN_EXCEPTION_SPEC(Eigen::eigen_assert_exception)
 #endif
   {
+    finished();
   }
 
   /** \returns the built matrix once all its coefficients have been set.