Attempt of fixing more child window operations.

src/Windows/Avalonia.Win32/Interop/UnmanagedMethods.cs

@@ -1017,6 +1017,9 @@ namespace Avalonia.Win32.Interop
         [DllImport("user32.dll")]
         public static extern bool ValidateRect(IntPtr hWnd, IntPtr lpRect);
 
+        [DllImport("user32.dll")]
+        public static extern bool IsWindow(IntPtr hWnd);
+        
         [DllImport("user32.dll")]
         public static extern bool IsWindowEnabled(IntPtr hWnd);
 
@@ -1050,6 +1053,9 @@ namespace Avalonia.Win32.Interop
         [DllImport("user32.dll")]
         public static extern bool ScreenToClient(IntPtr hWnd, ref POINT lpPoint);
 
+        [DllImport("user32.dll", SetLastError = true)]
+        public static extern IntPtr GetActiveWindow();
+        
         [DllImport("user32.dll", SetLastError = true)]
         public static extern IntPtr SetActiveWindow(IntPtr hWnd);
 

src/Windows/Avalonia.Win32/WindowImpl.AppWndProc.cs

@@ -65,7 +65,17 @@ namespace Avalonia.Win32
                             return IntPtr.Zero;
                         }
 
-                        _parent?.SetEnabled(true);
+                        if (_parent != null && IsWindow(_parent._hwnd))
+                        {
+                            var wasActive = GetActiveWindow() == _hwnd;
+
+                            _parent.SetEnabled(true);
+
+                            if (wasActive)
+                            {
+                                SetActiveWindow(_parent._hwnd);
+                            }
+                        }
 
                         break;
                     }