check against nil to load icon when albumart is not available

Sources/VLCLocalServerFolderListViewController.m

@@ -228,7 +228,7 @@
             [cell setSubtitle: [NSString stringWithFormat:@"%@ (%@)", [NSByteCountFormatter stringFromByteCount:mediaSize countStyle:NSByteCountFormatterCountStyleFile], [VLCTime timeWithInt:durationInSeconds * 1000].stringValue]];
             [cell setIsDirectory:NO];
             cell.isDownloadable = YES;
-            if (![mediaItem.albumArt isEqualToString:NULL])
+            if (mediaItem.albumArt != nil)
                 [cell setIconURL:[NSURL URLWithString:mediaItem.albumArt]];
             [cell setIcon:[UIImage imageNamed:@"blank"]];
             cell.delegate = self;