throw an error instead of falling back to getfield for Ptr types

[ghyatzo]

Hello,

The generated Base.getproperty(x::Ptr{T}, f::Symbol) emits a getfield(x,f) if all other cases are exhausted.
But getfield is not really defined for Ptr (which makes sense, since it doesn't have any field) and static analysis tools like JET generate a lot of noise about it.

What about throwing an exception instead? It shouldn't be breaking since we'd be throwing an exception anyway, and provides a better error message and makes analysis tools happy.

[Gnimuc]

This fallback pattern is used ubiquitously in Julia Base.

[ghyatzo]

Yes, It's a common pattern. And I think it makes absolute sense when overloading the getproperty of objects that do have fields.

But when used to give an isbits type virtual fields I think that same pattern is a bit misplaced.

Anyway, this is minor, it would just be to play nicer with static analyzers. I'll leave this here if you change your mind!