Fix attachment cover/contain again

The fix for chrome's stretched images broke wide images when using the option to use object-fit: cover, they would not fill the full height of the area. Now all attachment images look correct according to your settings (and videos when using the modal to play them).

Using 'cover' (this was broken before the previous fix)

Using 'contain'

Using 'cover' (this is currently broken in develop)

Using 'contain'

Nice css magic

merged

mentioned in commit 4acac3c3