Performance: attempt to fix actor leak

src/UI/Image/ImagePreview.svelte

@@ -25,6 +25,10 @@
 
   onDestroy(Zoomcontrol.createLock())
 
+  let destroyed = false
+  onDestroy(() => {
+    destroyed = true
+  })
   async function initPhotosphere() {
     const imageInfo: Feature<Point, PanoramaView> = await image.provider.getPanoramaInfo(image)
     if (imageInfo === undefined) {
@@ -37,6 +41,7 @@
     } else {
       nearbyFeatures.addCallbackAndRunD((feats) => {
         viewer.setNearbyFeatures(feats)
+        return destroyed
       })
     }
     isLoaded.set(true)