[Bug]: copying nodes with dynamic inputs throws console error

### Prerequisites

- [x] I am running the latest version of ComfyUI
- [x] I have searched existing issues to make sure this isn't a duplicate
- [ ] I have tested with all custom nodes disabled ([see how](https://docs.comfy.org/troubleshooting/custom-node-issues#step-1%3A-test-with-all-custom-nodes-disabled))

### What happened?

Attempting to copy a node with dynamic inputs throws a Litegraph error. Rolling back to frontend version 1.14.5 this works. As of version 1.15.0-> it now throws an error.

### Steps to Reproduce

1. Drop a node with dynamic inputs onto the canvas
2. Select the node
3. Press Ctrl-C

### How is this affecting you?

Feature doesn't work as expected

### ComfyUI Frontend Version

1.25.4

### Browser

Firefox

### Console Errors

```javascript
Uncaught NullGraphError: Attempted to access LGraph reference that was null or undefined.
NullGraphError litegraph.es.js:910
disconnectInput litegraph.es.js:5827
removeInput litegraph.es.js:4899
onConnectionsChange dynamicnode.js line 8 > srcScript:72
configure litegraph.es.js:4311
configure litegraphService.ts:607
clone litegraph.es.js:4399
copyToClipboard litegraph.es.js:10795
useCopy useCopy.ts:31
register2 index.mjs:213
stopWatch index.mjs:225
stopWatch index.mjs:225
stopWatch index.mjs:224
t3 vue.esm-browser.prod.js:5
t6 vue.esm-browser.prod.js:5
call vue.esm-browser.prod.js:5
T vue.esm-browser.prod.js:5
f vue.esm-browser.prod.js:5
iU vue.esm-browser.prod.js:5
iB vue.esm-browser.prod.js:5
useEventListener index.mjs:216
useCopy useCopy.ts:11
setup GraphCanvas.vue:291
rh vue.esm-browser.prod.js:5
t3 vue.esm-browser.prod.js:5
t6 vue.esm-browser.prod.js:5
__weh vue.esm-browser.prod.js:5
na vue.esm-browser.prod.js:5
e vue.esm-browser.prod.js:5
Caused by: undefined
```

### Logs

```shell

```

### Additional Context

_No response_