`check_hermitian` fails for zero-matrix

Hi!

As a follow-up to #76 and #78, I have an issue with hermitian checks for zero matrix. 

```julia
using MatrixAlgebraKit: check_hermitian,  default_hermitian_tol, eigh_full, ishermitian

m = zeros((1,1))
ishermitian(m)  # true
ishermitian(m; atol=default_hermitian_tol(m))  # false
check_hermitian(m)  # DomainError
eigh_full(m)  # DomainError
```
