On failure, doesn't clear previous image / title bar / overlay

When the loader fails to handle a directory (see issue #122) none of the existing state is cleared, except for the next / prev buttons. Namely, the title bar and overlay still show the last label displayed, and the last loaded image is still shown.

This implies to the user the old image list is still loaded, which is not the case.

Start at the loader failure path described in issue #122 and trace how the title bar, overlay, displayed image, and next/prev buttons are updated. Reproduce a failed directory load after displaying an image, then verify that all prior image and label state is cleared and the interface no longer implies that the old list is loaded.

Written by the indexing model from the issue text.