Sapling hangs indefinitely when multiple instances of VSCode are open

[RyanDillinger]

Describe the bug
First off, thank you so much for creating this visualization, it's a life saver.

Bug: (maybe not) sapling processing hangs indefinitely when I attempt to generate a tree if more than one instance of VS Code is open (specifically, different projects are open).

It's something I rarely do, so it's not a big deal. Why I decided to post this is because I happened to have two VS Code instances open when I first installed sapling. I couldn't understand why I could see the sapling sidebar icon, the right-click menu 'generate tree' option, and the status bar 'build tree' option, but the hierarchy tree never generated.

To Reproduce
Steps to reproduce the behavior:

1. Open two instances of VS Code (possibly need to be separate projects)
2. Click on 'sapling icon', or 'right-click' generate tree, or click status bar 'build tree'
3. See error

Expected behavior
Sapling sidebar doesn't open when choosing 'generate tree' or 'build tree'. Hierarchy tree doesn't generate/render when sidebar sapling icon is clicked. Notice when the sapling side bar is open, under VS Code '"Sidebar" title, the scrolling graphic renders (left to right) as if it's thinking about it (i.e., still processing).

Screenshots
N/A

Desktop (please complete the following information):

• OS: Ubuntu 20.04
• Versions: latest sapling and latest stable VS Code

Thanks again for providing a great React tool, keep up the good work!