`file_draw_preview()` does multiple things and is quite hard to follow
already, it needs some improvents. One issue is naming that I always
found made the function unnecessarily confusing. For example `is_icon`
had nothing to do with the `icon` parameter, you'd have to search around
the code a bit to understand what it was actually representing.
Attempt to make variable and function names more clear.
Also reduce variable scope and add a comment.
9a6beb915d