fix(web): restore timeline scroll when the asset id cannot be resolved (#30916)

Co-authored-by: Daniel Dietzler <mail@ddietzler.dev>
Co-authored-by: Daniel Dietzler <36593685+danieldietzler@users.noreply.github.com>

web/src/lib/components/timeline/Timeline.svelte

@@ -210,13 +210,13 @@
     }
     const scrollTarget = assetViewerManager.gridScrollTarget?.at;
     const scrolled = scrollTarget ? await scrollAndLoadAsset(scrollTarget) : false;
-    if (!scrolled) {
-      // if the asset is not found, scroll to the top
-      timelineManager.scrollTo(0);
-    } else if (scrollTarget) {
+    if (scrolled && scrollTarget) {
       await tick();
       focusAsset(scrollTarget);
+    } else {
+      timelineManager.scrollTo(lastVisibleScrollTop);
     }
+
     invisible = false;
   };
 
@@ -224,6 +224,9 @@
   let initialLoadWasAssetViewer: boolean | null = null;
   // only modified in beforeNavigate()
   let hasNavigatedToOrFromAssetViewer: boolean = false;
+  // The layout sets `display: none` on this subtree while the viewer is open.
+  // Browsers drop the scroll offset of a hidden element.
+  let lastVisibleScrollTop = 0;
 
   // beforeNavigate is only called AFTER a svelte route has already been loaded
   // and a new route is being navigated to. It will never be called on direct
@@ -309,6 +312,9 @@
     if (!scrollableElement) {
       return;
     }
+    if (!assetViewerManager.isViewing) {
+      lastVisibleScrollTop = scrollableElement.scrollTop;
+    }
 
     if (timelineManager.limitedScroll) {
       // edge case - scroll limited due to size of content, must adjust -  use the overall percent instead