MainWindow: Fix unsaved dialog is shown after saving (take 2)

Alternative to #141

src/MainWindow.vala

@@ -89,6 +89,7 @@ public class MainWindow : Adw.ApplicationWindow {
         });
 
         edit_view.file_updated.connect (() => {
+            desktop_file.copy_to (backup_desktop_file);
             overlay.add_toast (updated_toast);
         });
 
@@ -158,7 +159,8 @@ public class MainWindow : Adw.ApplicationWindow {
 
     public void show_edit_view (Model.DesktopFile file) {
         desktop_file = file;
-        backup_desktop_file = new Model.DesktopFile.copy (file);
+        backup_desktop_file = new Model.DesktopFile (desktop_file.path);
+        desktop_file.copy_to (backup_desktop_file);
 
         edit_view.load_file (desktop_file);
         leaflet.show_content = true;

src/Model/DesktopFile.vala

@@ -30,16 +30,6 @@ public class Model.DesktopFile : Object {
         );
     }
 
-    /**
-     * The copy constructor.
-     *
-     * @param other Another DesktopFile.
-     */
-    public DesktopFile.copy (DesktopFile other) {
-        string data = other.to_data ();
-        load_from_data (data);
-    }
-
     construct {
         keyfile = new KeyFile ();
     }
@@ -58,6 +48,17 @@ public class Model.DesktopFile : Object {
         return this_data == other_data;
     }
 
+    /**
+     * Copy and set data from this to another DesktopFile.
+     *
+     * @param dest Another DesktopFile to copy this data to.
+     * @return true if successfully copied, false otherwise.
+     */
+    public bool copy_to (DesktopFile dest) {
+        string data = to_data ();
+        return dest.load_from_data (data);
+    }
+
     ////////////////////////////////////////////////////////////////////////////
     //
     // Key Opearations