Sailfish: do not crash when opening an audio folders

The QML side attempted to simply pass all items of type 'Audio' to the
PlaybackManager.playItem(). This does not work for folders and it will
crash. This does not fix the presentation of audio folders/playlists,
but it does fix the crash.

sailfish/qml/harbour-sailfin.qml

@@ -151,7 +151,7 @@ ApplicationWindow {
     }
 
     function navigateToItem(jellyfinId, mediaType, type, isFolder) {
-        if (mediaType === "Audio") {
+        if (mediaType === "Audio" && !isFolder) {
             playbackManager.playItemId(jellyfinId)
         } else {
             pageStack.push(Utils.getPageUrl(mediaType, type, isFolder), {"itemId": jellyfinId});