Disable thumbfast for images

[AndyM48]

Sounds a bit daft but we can:

# Enable on network playback
network=no

# Enable on audio playback
audio=no

but we cannot disable thumbfast for images.

There is some conflict when it comes to .gif images, sometimes they are treated as image files and sometimes videos, this also applies to uosc. Mpv recognises them as images so a profile can be used to pass specific options, e.g:

[image]
# a profile to loop image files to cater for gifs
loop-file=inf

which works tolerably well. However showing thumbnails over a .gif file is something of a distraction.