window: Resize to natural on map

Only at this point we can be certain about the screen info like size an
scaling factor.

src/widgets/image.rs

@@ -197,7 +197,7 @@ mod imp {
         /// Currently EXIF data
         pub(super) metadata: RefCell<Metadata>,
 
-        #[property(get)]
+        #[property(get=Self::image_size_available)]
         _image_size_available: bool,
 
         /// Current pointer position

src/widgets/image/metadata.rs

@@ -80,6 +80,10 @@ impl imp::LpImage {
             self.emmit_metadata_changed();
         }
     }
+
+    pub(super) fn image_size_available(&self) -> bool {
+        self.obj().image_size() > (0, 0)
+    }
 }
 
 impl LpImage {