fix race condition index out of bound crash in gridview

ui/widgets/gridview.go

@@ -129,11 +129,11 @@ func (g *GridView) Clear() {
 func (g *GridView) Reset(iter GridViewIterator) {
 	g.itemsMutex.Lock()
 	g.items = nil
-	g.itemsMutex.Unlock()
 	g.fetching = false
 	g.done = false
 	g.highestShown = 0
 	g.iter = iter
+	g.itemsMutex.Unlock()
 	g.fetchMoreItems(36)
 }
 
@@ -194,8 +194,13 @@ func (g *GridView) doUpdateItemCard(itemIdx int, card *GridViewItem) {
 	if itemIdx > g.highestShown {
 		g.highestShown = itemIdx
 	}
+	var item GridViewItemModel
 	g.itemsMutex.RLock()
-	item := g.items[itemIdx]
+	// itemIdx can rarely be out of range if the data is being updated
+	// as the view is requested to refresh
+	if itemIdx < len(g.items) {
+		item = g.items[itemIdx]
+	}
 	g.itemsMutex.RUnlock()
 	if card.PrevID == item.ID {
 		// nothing to do
@@ -208,6 +213,7 @@ func (g *GridView) doUpdateItemCard(itemIdx int, card *GridViewItem) {
 		card.ImgLoadCancel()
 		card.ImgLoadCancel = nil
 	}
+	if item.CoverArtID != "" {
 		if img, ok := g.imageFetcher.GetCoverThumbnailFromCache(item.CoverArtID); ok {
 			card.Cover.SetImage(img)
 		} else {
@@ -229,6 +235,10 @@ func (g *GridView) doUpdateItemCard(itemIdx int, card *GridViewItem) {
 				}
 			}(ctx)
 		}
+	} else {
+		// use the placeholder image for an item that has no cover art ID
+		card.Cover.SetImageResource(res.ResAlbumplaceholderPng)
+	}
 
 	// if user has scrolled near the bottom, fetch more
 	if !g.done && !g.fetching && itemIdx > g.lenItems()-10 {