fix: simplify null check for gallery subject in GalleryPhotoView

lib/widgets/gallery_photo_view.dart

···
                                   final gallery = widget.gallery;
                                   final subject = gallery?.uri;
                                   final focus = photo.uri;
-                                  if (subject == null || focus == null) {
+                                  if (subject == null) {
                                     return;
                                   }
                                   // Use the provider's createComment method