Hello,

I was playing with random matrices when I noticed this strange behaviour :

```
julia> using LinearAlgebra
julia> a=randn(10,11);
julia> isposdef(a*a')
true
julia> isposdef(a'*a)
false
```

I expected to have either way positive definite matrices since both matrices can be seen as covariance matrices of random data.

Am I doing something wrong here ?