Issuable sidebar opens, closes for small screens, ignoring stored state

How to reproduce:

1. On a mobile device (or a desktop browser size down), navigate to an Issuable (MR or Issue)
2. Open the sidebar
3. Refresh the page
4. Notice that the sidebar flies out momentarily, and is then hidden immediately. Depending on the performance capabilities of your device, it will be more or less noticeable.

I'm not sure if the intended behavior is to always hide the sidebar on page reload for small devices, or if this is just a bug. But if this is intended, we need to keep this sidebar collapsed, rather than allowing it to fly open and shut momentarily.

cc: @jschatz1 @lbennett