Group node convert input to widget break things badly

To reproduce:

- load default workflow
- on one of the CLIP text encode, convert text to input
- convert the two CLIP encodes, the sampler, and the VAE decode, to a group node
- on the group node, convert CLIP text encode text to widget
- convert group node to node

Result:

- the group node still exists and the workflow is broken
- Javascript console has:
```
groupNode.js:770 Uncaught TypeError: Cannot read properties of undefined (reading 'link')
at reconnectInputs (groupNode.js:770:16)
at GroupNodeHandler.node.convertToNodes (groupNode.js:795:4)
at HTMLDivElement.callback (groupNode.js:812:18)
at HTMLDivElement.inner_onclick (litegraph.core.js:13924:44)
```