Scroll calcs are not right in discourse

### Current Behavior

Some flows are not rendered and are not visible until zoom level is very small.

From the forum: https://discourse.nodered.org/t/sharing-flows-on-the-forum-just-get-prettier/97957/28?u=steve-mcl

> Regarding this empty flow view on [Neo-pixel LED, heart beat. Help - #2 by Trying_to_learn](https://discourse.nodered.org/t/neo-pixel-led-heart-beat-help/97990/2) and [Idea: Add a node.js LTS check to Node-RED? - #3 by TotallyInformation](https://discourse.nodered.org/t/idea-add-a-node-js-lts-check-to-node-red/96980/3) they both render correctly when I run them flows in the source code version of the flow viewer

### Expected Behavior

Should auto scroll & auto zoom to the "best fit"

### Steps To Reproduce

visit any of the flows linked above
inspect the HTML of the SVG (the nodes are present)

### Environment

- FlowFuse version:
- Node.js version:
- npm version:
- Platform/OS:
- Browser:

### Linked Customers

- Customer name and/or link to HubSpot contact