Fix compiling C# scripts that use nuget package to properly resolve it on 1st build

Source/Tools/Flax.Build/Build/DotNet/Builder.DotNet.cs

@@ -284,9 +284,17 @@ namespace Flax.Build
             if (buildData.TargetOptions.NugetPackageReferences.Any())
             {
                 var nugetPath = Utilities.GetNugetPackagesPath();
+                var restoreOnce = true;
                 foreach (var reference in buildOptions.NugetPackageReferences)
                 {
                     var path = reference.GetLibPath(nugetPath);
+                    if (!File.Exists(path) && restoreOnce)
+                    {
+                        // Package binaries folder is missing so restore packages (incl. dependency packages)
+                        RestoreNugetPackages(graph, buildOptions.Target, buildOptions);
+                        restoreOnce = false;
+                        path = reference.GetLibPath(nugetPath);
+                    }
                     args.Add(string.Format("/reference:\"{0}\"", path));
                 }
             }

Source/Tools/Flax.Build/Build/NativeCpp/BuildOptions.cs

@@ -139,7 +139,9 @@ namespace Flax.Build.NativeCpp
         {
             if (libFolder == null)
                 libFolder = GetLibFolder(nugetPath);
-            var dlls = Directory.GetFiles(libFolder, "*.dll", SearchOption.TopDirectoryOnly);
+            if (libFolder == string.Empty)
+                return string.Empty;
+            var dlls = Directory.Exists(libFolder) ? Directory.GetFiles(libFolder, "*.dll", SearchOption.TopDirectoryOnly) : [];
             if (dlls.Length == 0)
             {
                 Log.Error($"Missing NuGet package \"{Name}, {Version}, {Framework}\" binaries (folder: {libFolder})");