[BUG] Posts without placeholder image don't render correctly in template

[alexkisielewicz]

Describe the bug
Bootstrap cards for posts without uploaded images are not displayed correctly.

To Reproduce
Steps to reproduce the behavior:

1. Go to 'index page'
2. Scroll down to section 'Top 3 liked posts'
3. See error

Simillar code is used for user dashboard in user_account.html

[alexkisielewicz]

Bug fixed by adding if-else statement to display placeholder if featured_image is not available.