Fix runtime exception

(cherry picked from commit 2a5873b95c7488643e871073c6ec6b6ae3fed34c)

Sources/VLCLibraryViewController.m

@@ -657,6 +657,8 @@ static NSString *kUsingTableViewToShowData = @"UsingTableViewToShowData";
             return;
         object.folderTrackNumber = @(toIndexPath.item - 1);
         object = [_foundMedia objectAtIndex:fromIndexPath.item];
+        if (![object isKindOfClass:[MLFile class]])
+            return;
         object.folderTrackNumber = @(fromIndexPath.item - 1);
     }
 }