Folder names that end in .ino are recognized as a sketch by the Arduino IDE

Don't as why, but I found a folder structure like this in my sketchbook:
`folder/folder.ino/folder.ino`. Where the first "folder.ino" is obviously a folder and not a file. However it is recognized as file and via `file->sketchbook` you can try to open it, but it will fail of course.

I think the question why i have this structure will be unanswered. I don't know what I did there.

Reproduce the reported sketchbook structure `folder/folder.ino/folder.ino` and open it through `File → Sketchbook`. Trace the sketchbook entry handling that treats the `.ino`-named folder as a file; done means the folder is not presented as an openable sketch and valid sketches still appear normally.

Written by the indexing model from the issue text.