fix: Clean Remuxes task fails when primary user is empty.

Author: katiekloss

Jellyfin.Plugin.DoViRemux/CleanRemuxesTask.cs

@@ -31,7 +31,7 @@ public async Task ExecuteAsync(IProgress<double> progress, CancellationToken can
             ?? throw new Exception("Can't get plugin instance");
 
         var configuration = plugin.Configuration;
-        if (configuration.PrimaryUser is null)
+        if (string.IsNullOrEmpty(configuration.PrimaryUser))
         {
             return;
         }