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 {
+    pub fn content_provider(&self) -> Option<gdk::ContentProvider> {
-        let imp = self.imp();
+        let file = self.file()?;
-        let mut contents = vec![];
+        let list = gdk::FileList::from_array(&[file]);
-
+        Some(gdk::ContentProvider::for_value(&list.to_value()))
-        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())
     }
 }

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())
                     }
                 }),
             );