Fix upload after comment preview bug

What does this MR do and why?

Fixes the bug described in Attaching a file by clicking the markdown edito... (#438396 - closed)

How to set up and validate locally

• Go to an issue
• Edit description
• Upload an image (using Attach a file or image button)
• Click Preview
• Go back to edit
• Upload another image
• Success!

Links

• ✂️ UX Paper Cuts 17.3 → Dark mode - Design Support (#452231 - closed)
• Closes Attaching a file by clicking the markdown edito... (#438396 - closed)