filechooser: Fix a crash when using a file as the path

[ZingBallyhoo]

Currently, if you select a file (not a folder) in filechooser, and then open a new filechooser using the same path, you will get a crash, because it expects a folder. Most noticeable when using kivy.uix.settings.SettingPath, as you can select a file, and the next time you try and change that setting, the filechooser will be completely blank.

This is just a simple fix that:

• Checks to see if the path is a file
• If it is, it will load the parent directory, instead of trying to use the file like a folder