Fix os check warning.

src/NTwain/OperatingSystem.cs

@@ -8,9 +8,40 @@ namespace NTwain;
 /// </summary>
 static class OperatingSystem
 {
-    public static bool IsWindows()
+    static readonly bool _isWindows = Environment.OSVersion.Platform == PlatformID.Win32NT;
+
+    public static bool IsWindows() => _isWindows;
+
+    // copied from .net logic
+
+    public static bool IsWindowsVersionAtLeast(int major, int minor = 0, int build = 0, int revision = 0)
+            => IsWindows() && IsOSVersionAtLeast(major, minor, build, revision);
+
+    private static bool IsOSVersionAtLeast(int major, int minor, int build, int revision)
     {
-        return Environment.OSVersion.Platform == PlatformID.Win32NT;
+        Version current = Environment.OSVersion.Version;
+
+        if (current.Major != major)
+        {
+            return current.Major > major;
+        }
+        if (current.Minor != minor)
+        {
+            return current.Minor > minor;
+        }
+        // Unspecified build component is to be treated as zero
+        int currentBuild = current.Build < 0 ? 0 : current.Build;
+        build = build < 0 ? 0 : build;
+        if (currentBuild != build)
+        {
+            return currentBuild > build;
+        }
+
+        // Unspecified revision component is to be treated as zero
+        int currentRevision = current.Revision < 0 ? 0 : current.Revision;
+        revision = revision < 0 ? 0 : revision;
+
+        return currentRevision >= revision;
     }
 }
 #endif

src/NTwain/TwainAppSession.cs

@@ -334,7 +334,8 @@ namespace NTwain
                         {
                             try
                             {
-                                _ = CloseDSMAsync();
+                                if (OperatingSystem.IsWindowsVersionAtLeast(5, 1, 2600))
+                                    _ = CloseDSMAsync();
                             }
                             catch (InvalidOperationException) { }
                         }