fix: get active window issue.

src/Shared/HandyControl_Shared/Tools/Interop/InteropMethods.cs

@@ -348,6 +348,9 @@ internal class InteropMethods
     [DllImport(InteropValues.ExternDll.User32)]
     internal static extern IntPtr GetWindow(IntPtr hwnd, int nCmd);
 
+    [DllImport(InteropValues.ExternDll.User32)]
+    internal static extern IntPtr GetActiveWindow();
+
     [DllImport(InteropValues.ExternDll.User32)]
     [return: MarshalAs(UnmanagedType.Bool)]
     internal static extern bool IsWindowVisible(IntPtr hwnd);