Dear Maintainer,

Thumbanail cache doesn't work properly. It takes every time a lot of time to
display thumbnails during entering forlders (it refreshes folders every time).
If I clear .thumbanils folder, launch Gwenview, and open some folders it
creates thumbanils only one time (thumbs are created in cache). When I launch
Gwenview once again thumbnail are displayed quicly. In this case it works
properly.
But when I open some other folder first with Dophin and display thumbnails in
it, and then launch Gwenview in the same folder, the problem returns.
It looks like Gwenview can't use thumbnails created by Dolphin and evan can't
recreate them in cache.