fix: switch os.pathsep constant with os.sep

Finding files in few formats always fail because of wrong path.
Example:
When finding poster file for media file **Z:\Filmy\Cyborg Girl (2008)\Cyborg Girl (2008) - Part01.avi**
It tries these:
1. Z:\Filmy\Cyborg Girl (2008)\Cyborg Girl (2008) - Part01-poster.jpg
2. **Z:\Filmy\Cyborg Girl (2008);Z:\Filmy\Cyborg Girl (2008)-poster.jpg**
3. **Z:\Filmy\Cyborg Girl (2008);Z:\Filmy\Cyborg Girl-poster.jpg**
4. Z:\Filmy\Cyborg Girl (2008)\poster.jpg
5. Z:\Filmy\Cyborg Girl (2008)\Cyborg Girl (2008) - Part01.tbn