For loops with the syntax for i in iter

For loops with the syntax `for i in iter` dont work even with a simple iterator like a Vector.
MWE
```julia
using LoopVectorization

test = rand(10000)
function mymean(func,iter)
len = length(iter)
total = zero(eltype(iter))
@avx for i in iter
total += func(i)
end
total/len
end

mymean(identity,test)
```

This gives this error:
```julia
ERROR: LoadError: MethodError: no method matching canonicalize_range(::Vector{Float64})
```

Start with the @avx loop handling and the canonicalize_range(::Vector{Float64}) failure shown by the MWE. Trace how iterable forms are canonicalized, then verify that the provided mymean example with a Vector completes successfully.

Vom Indexierungsmodell aus dem Issue-Text verfasst.