[Android] Fix a situation within the FolderBrowser where the application would crash. listFiles() returns null when either the File object it's called on isn't a directory or if an I/O error happens (in their infinite wisdom, they actually thought NOT throwing an exception was a cool way to handle this. How about that?). In the case of trying to access system directories as a normal user, an I/O error will occur due to permission access rights. This fixes that.