Fix StringLoader GetString

Author: AliveDevil

Packages.props

@@ -25,7 +25,7 @@
     <PackageReference Update="Microsoft.Toolkit.Uwp.Notifications" Version="7.1.2" />
     <PackageReference Update="Microsoft.Windows.CsWin32" Version="0.3.106" />
     <PackageReference Update="Microsoft.Windows.SDK.Contracts" Version="10.0.22000.196" />
-    <PackageReference Update="NUnit" Version="4.1.0" />
+    <PackageReference Update="NUnit" Version="4.2.0" />
     <PackageReference Update="NUnit.Console" Version="3.17.0" />
     <PackageReference Update="NUnit3TestAdapter" Version="4.5.0" />
     <PackageReference Update="ObjectListView.Official" Version="2.9.1" />

core/src/main/csharp/Windows/Win32/PCWSTR.cs

@@ -15,5 +15,5 @@ public static PCWSTR DangerousFromSpan(in ReadOnlySpan<char> value)
 
     public PWSTR DangerousAsPWSTR() => Value;
 
-    public string ToString(int length) => Value is null ? new string(Value, 0, length) : null;
+    public readonly string ToString(int length) => Value is null ? null : new string(Value, 0, length);
 }

core/src/test/csharp/ch/cyberduck/core/I18n/StringLoaderTest.cs

@@ -0,0 +1,16 @@
+using Ch.Cyberduck.Core.I18n;
+using NUnit.Framework;
+
+namespace Cyberduck.Core.Test.I18n
+{
+    [TestFixture]
+    public class StringLoaderTest
+    {
+        [Test]
+        public void LoadString()
+        {
+            using StringLoader stringLoader = new();
+            Assert.That(stringLoader.GetString(30396u), Is.Not.WhiteSpace);
+        }
+    }
+}