image_view: Handle target file gone correctly

Before, if the target file was gone, files_around just returned an empty
list of files, leading Loupe to think there are no images and showing
the empty state view.

This was frequently triggered by the "Replace original" function in
editing, since the tmp file was already gone, when the view moved to it.

Now, the correct error is shown, and scrolling to the other files is
possible.

Issue #585

src/metadata.rs

@@ -28,10 +28,9 @@ use chrono::prelude::*;
 pub use file::FileInfo;
 use glib::TimeZone;
 use glycin::{Frame, FrameDetails, ImageDetails, MemoryFormat};
-use gufo::common::cicp;
 use gufo::common::datetime::DateTime;
 use gufo::common::orientation::Orientation;
-use gufo::common::physical_dimension;
+use gufo::common::{cicp, physical_dimension};
 
 use crate::deps::*;
 use crate::util;