Can't navigate overloads with arrow keys - regression

Is this a BUG REPORT or FEATURE REQUEST? (choose one):
Bug report

What happened:
When the popup for multiple overload suggestions is open, the up and down arrow keys move around the editor instead of navigating between overloads.

This has been tested with .NET Core project while editing a C# file.

The bug seems to be a regression of the one already mentioned in #985; the fix seems to have stopped working.

I have also tried adding the up and down keys to the vim.handleKeys section of my config file with no success.

What did you expect to happen:
When pressing the up or the down key, with the popup open, the other suggestions should be shown

How to reproduce it (as minimally and precisely as possible):

(Note: there might be easier ways to test it, this is the quickest I could come up with)

Step 1-3 are necessary only if there's a need for a fresh new project

1. Create a new dotnet core console project: dotnet new console --name Test
2. Open the Test folder with vscode
3. Let vscode add the necessary assets
4. Use, for Program.cs, the following minimal program:

namespace Test
{
    class Program
    {
        static void Main(string[] args) => Foo();

        static bool Foo() => Foo("");
        static bool Foo(string text) => true;
    }
}

5. Move the cursor to line 5: static void Main(string[] args) => Foo(|);
6. Press ctrl+shift+space to show the popup
7. When pressing the down arrow, the second overload should be shown; instead, the cursor moves down a line

Environment:

• Extension Version: 0.11.5
• OS Version: Linux x64 4.10.0-42-generic
• VSCode version: 1.23.0

Reproduce the issue in VSCodeVim with the provided C# overload example, using Ctrl+Shift+Space and the arrow keys. Trace the extension's arrow-key handling and the vim.handleKeys configuration; done means the popup switches between overloads without moving the editor cursor.