Typed hvcat doesn't handle UniformScaling

While `Float64[1 0; 0 1]`, `Float64[matrix; matrix]` and `[1I 0I; 0I matrix]` (with a matrix such as `matrix = [1 2; 3 4]`) all work fine, the following errors.

```
julia> Float64[1I 0I; 0I matrix]
ERROR: MethodError: Cannot `convert` an object of type UniformScaling{Int64} to an object of type Float64
```

I'm assuming this is unintended?