Error when closing a split pane in insert mode

Describe the bug
When executing the "Close all editors" command when in insert mode and with a split pane, the following error message is displayed:

TaskQueue: Error running task. Cannot read property 'options' of undefined.

To Reproduce
Steps to reproduce the behavior:

1. Open multiple files with a split pane
2. Enter insert mode
3. Execute the "Close all editors", command either via keyboard shortcut or the command pane

Expected behavior
No error message.

Screenshots
Here's a video showing the bug in action. First I show how no error message is displayed if in visual mode, then I show how an error message is displayed when in insert mode.

https://monosnap.com/file/nIvJhCv7JTDTaVMbXGUr8YgQ9qHHzH

Environment (please complete the following information):

• Extension (VsCodeVim) version: 1.0.8
• VSCode version: 1.31.1
• OS: macOS 10.14.3 - Darwin x64 18.2.0

Start by reproducing the reported sequence in VSCode: open multiple files in a split pane, enter insert mode, and run “Close all editors” via a shortcut or the command pane. Trace the command until the TaskQueue error occurs; done means the command closes the editors without displaying an error in insert mode.