Saving an empty workflow breaks the canvas and the workflow

[davelopez]

This happens only in dev as far as I could tell, so something recent must have broken it.
The issue is that the canvas (grid) is somehow gone and you can place nodes but you cannot move them around, and if you try to save the workflow, the API will throw a 500 because the step positions are "None".

Galaxy Version and/or server at which you observed the bug
Galaxy Version: dev
Commit: (run git rev-parse HEAD if you run this Galaxy server)

Browser and Operating System
Operating System: Windows, Linux, macOS
Browser: Firefox, Chrome, Chrome-based, Safari

To Reproduce
Steps to reproduce the behavior:

1. Go to http://127.0.0.1:8081/workflows/list
2. Click on Create to create a new workflow
3. Without adding any node, click Save & Exit
4. Open for edit the workflow you just created
5. Observe the canvas grid is gone (white screen instead of blue grid)
6. You can insert but cannot move around nodes
7. Saving the workflow will give a 500 error (due to missing step positions)

Expected behavior
The workflow is saved without steps and can be reopen and edited without issue.

Screenshots