As mentioned in cd13f52e75, e072853e63, fb6ac24514 and 9a6beb915d,
`file_draw_preview()` is a rather overloaded and confusing function. I'm
trying to make it more readable.
With the previous changes and all the other logic extracted, it's pretty clear
that the "special icon" drwaing (for the larger folder/file icon with the
folder/file type icon overlayed) also should be split off. Most remaining logic
in `file_draw_preview()` was either for the special icons or normal previews,
but not much code was shared within the function.
Tried to not cause user visible changes. There's a few pixel change in the
horizontal icon placement, but that's because it's centered properly now.
Previously it was just eyeballed I guess.
9e1f02dd4d