OK button behaviour is incorrect

[io7m]

The current code performs some checks in the onOKSelected method of the chooser view controller, and silently does nothing if those checks fail. These checks should not be performed there; the button should not be enabled in the first place if the checks have failed.

[io7m]

For example: Open a file chooser in CREATE mode. Specify a file selection mode function that only returns true if the target file is a regular file. If the user types the name of a nonexistent file (which they might do if they're looking to create a new file) this will always fail, and resultTarget will be set to an empty list. The subsequent checks that determine if the list is non-empty will fail, and the whole method will return silently.