Fix a bug for operation between a 4x1 matrix and a scalar

Hi, 

This pull request fixes a bug (issue 2788) I reported. When a 4x1 matrix is added with a Scalar by arithm_op(), they are previously treated as two 4x1 matrix added together. But the scalar should be added to each element of the 4x1 matrix. 

I added some check for avoid the bug.