fixes

Author: X39

source/X39.UnitedTacticalForces.Api/Services/GameServerController/Controllers/SteamGameServerControllerBase.cs

@@ -674,8 +674,10 @@ await UpdateStreamService.SendUpdateAsync(
             );
             var workingDir = Path.Combine(
                 installPath,
+                "mods",
                 workshopId.ToString()
             );
+            Directory.CreateDirectory(workingDir);
             var psi = new ProcessStartInfo
             {
                 FileName               = depotDownloaderPath,