PlaylistEditorView: make sure we only update the images once in itemV…

…isible

If no image could be found for a node each time a node becomes visible we
would retry to find one. This uses a text field as a flag to make sure we
only look for an image the first time a node becomes visible.

mythplugins/mythmusic/mythmusic/playlisteditorview.cpp

@@ -837,8 +837,10 @@ void PlaylistEditorView::treeItemVisible(MythUIButtonListItem *item)
     if (!mnode)
         return;
 
-    if (item->GetImageFilename().isEmpty())
+    if (item->GetText("*").isEmpty())
     {
+        item->SetText(" ", "*");
+
         QString artFile;
 
         if (mnode->getAction() == "trackid")