Thumbnails loading times increases as you reach the bottom of big playlists

Description

The first entries of a playlist load the thumbnails pretty fast but as you go down in the list the time to load a thumbnail gets longer and longer

This is specially visible in ozone with 2000 entries in a playlist. It also happens in rgui and glui but it is less annoying since these two menu drivers wait a few miliseconds before loading the thumbnail (this option is not available in ozone)

Expected behavior

Loading the thumbnail of the first entry on the list and on the last one should take the same time

Actual behavior

Loading thumbnails at the end of a big playlist takes a lot of time compared to the first entries

Steps to reproduce the bug

1. Create a playlist with 2000 entries (the full romset snes playlist)
2. Configure thumbnails
3. Start navigating the playlist, thumbnails loading times are small
4. Go to letter Z and compare

Bisect Results

Not sure when this started to happen, but it's been there in the recent releases

Version/Commit

• RetroArch: 1.8.7 stable

Environment information

• OS: I am testing this on the Nintendo Switch, but it's very likely that it's happening in all platforms

Reproduce the slowdown with a 2,000-entry playlist, configured thumbnails, and navigation to the end of the list, comparing ozone with rgui and glui. Start by tracing thumbnail loading in the menu-driver paths; done means thumbnails near the beginning and end load in comparable times across the affected drivers.