image: Use FileList in ContentProvider

Makes dragging an image out of Loupe work in most cases.
There seems to be an issue with dragging from flatpak to host.
Removing the png from the provider seems to avoid gdk crashes
but not 100% sure that was the cause.

src/widgets/image.rs

@@ -905,21 +905,9 @@ impl LpImage {
     }
 
     /// Drag and drop content provider
-    pub fn content_provider(&self) -> gdk::ContentProvider {
-        let imp = self.imp();
-        let mut contents = vec![];
-
-        if let Some(file) = imp.file.borrow().as_ref() {
-            let content = gdk::ContentProvider::for_value(&file.to_value());
-            contents.push(content);
-        }
-
-        if let Some(texture) = imp.texture.borrow().as_ref() {
-            let bytes = texture.save_to_png_bytes();
-            let content = gdk::ContentProvider::for_bytes("image/png", &bytes);
-            contents.push(content);
-        }
-
-        gdk::ContentProvider::new_union(contents.as_slice())
+    pub fn content_provider(&self) -> Option<gdk::ContentProvider> {
+        let file = self.file()?;
+        let list = gdk::FileList::from_array(&[file]);
+        Some(gdk::ContentProvider::for_value(&list.to_value()))
     }
 }

src/widgets/image_page.rs

@@ -159,7 +159,7 @@ impl LpImagePage {
         self.imp().image.texture()
     }
 
-    pub fn content_provider(&self) -> gdk::ContentProvider {
+    pub fn content_provider(&self) -> Option<gdk::ContentProvider> {
         self.imp().image.content_provider()
     }
 

src/widgets/image_view.rs

@@ -126,7 +126,7 @@ mod imp {
                         gesture.set_state(gtk::EventSequenceState::Denied);
                         None
                     } else {
-                        obj.current_page().map(|p| p.content_provider())
+                        obj.current_page().and_then(|p| p.content_provider())
                     }
                 }),
             );