Another codegen error involving instance variables with Iterator type

[HertzDevil]

Taken from straight-shoota/crinja#70:

class Crinja
  module Object
  end

  alias Raw = Int32 | Crinja::Object | Array(Value)

  struct Value
    getter raw : Raw

    def initialize(@raw : Raw)
    end

    def raw_each
      case object = @raw
      when Iterable(Value)
        RawIterator.new(object.each)
      else
        raise RuntimeError.new("#{object.class} is not iterable")
      end
    end

    class RawIterator
      include Iterator(Raw)

      def initialize(@iterator : Iterator(Value))
      end

      def next
        case value = @iterator.next
        when Value
          value.raw
        else
          stop
        end
      end
    end
  end

  class Tuple
    include Indexable(Value)
    include Object

    def unsafe_fetch(index : Int)
      Crinja::Value.new(1)
    end

    def size
      1
    end
  end
end

struct StructWithIterator
  include Crinja::Object
  include ::Iterable(Crinja::Value)

  def each
    iter = uninitialized Iterator(Crinja::Value)
    iter
  end
end

# also crashes with an invalid memory access sometimes
Crinja::Value.new(Crinja::Tuple.new).raw_each.next # => #<Iterator::Stop:0x7f24db1b8fe0>

The above should print 1 instead. The error goes away if either include inside StructWithIterator is removed, or if StructWithIterator#each returns a more specific type like [Crinja::Value.new(1)].each. This might be related to #7044 or #10967.