Check for empty object (#8075)

## Summary

<!-- One sentence describing what changed and why. -->

## Changes
- **What**: <!-- Core functionality added/modified -->
PNG images causes getWorkflowDataFromFile() to return an empty object,
added a check to handle it.

## Review Focus
<!-- If this PR fixes an issue, uncomment and update the line below -->
<!-- Fixes #ISSUE_NUMBER -->
I don't think it exists yet? From Slack Conversation. Just make sure to
use a PNG image and not a JPEG disguised as a PNG.

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-8075-Check-for-empty-object-2e96d73d3650816b8812eb7244b48f1a)
by [Unito](https://www.unito.io)

src/scripts/app.ts

@@ -1433,7 +1433,7 @@ export class ComfyApp {
   async handleFile(file: File, openSource?: WorkflowOpenSource) {
     const fileName = file.name.replace(/\.\w+$/, '') // Strip file extension
     const workflowData = await getWorkflowDataFromFile(file)
-    if (!workflowData) {
+    if (_.isEmpty(workflowData)) {
       if (file.type.startsWith('image')) {
         const transfer = new DataTransfer()
         transfer.items.add(file)