Blog list does not show jpeg images, but shows jpg

## Describe the bug
If you set the post image as a jpeg image, it shows in the blog post but not in the blog list, renaming it to .jpg makes it work again.

## Software Versions
- DNN: 06.04.01
- Module: 09.02.01

## To Reproduce
Steps to reproduce the behavior:
1. Create a blog post
2. In the Summary and Metadata tab, set a .jpeg image (must be with the 4 letter extension)

## Expected behavior
The image should show in the list of blog posts.

## Additional context
Renaming and reuploading it with .jpg extension fixes the issue, but jpeg should be a supported file extension.