Multi-Monitor DPI scaling breaks dialog sizes (#15304)

* Multi-Monitor DPI scaling breaks dialog sizes

* move the flag up

* second location

src/Avalonia.Controls/Window.cs

@@ -93,6 +93,7 @@ namespace Avalonia.Controls
         private bool _isExtendedIntoWindowDecorations;
         private Thickness _windowDecorationMargin;
         private Thickness _offScreenMargin;
+        private bool _canHandleResized = false;
 
         /// <summary>
         /// Defines the <see cref="SizeToContent"/> property.
@@ -722,6 +723,8 @@ namespace Avalonia.Controls
                 // thus we ought to call it again later to center window correctly if needed, when scaling will be already applied
                 SetWindowStartupLocation(owner);
 
+                _canHandleResized = true; 
+                
                 var initialSize = new Size(
                     double.IsNaN(Width) ? Math.Max(MinWidth, ClientSize.Width) : Width,
                     double.IsNaN(Height) ? Math.Max(MinHeight, ClientSize.Height) : Height);
@@ -800,6 +803,8 @@ namespace Avalonia.Controls
                 // determined only by calling this method. But here it will calculate not precise location because scaling may not yet be applied (see i.e. X11Window),
                 // thus we ought to call it again later to center window correctly if needed, when scaling will be already applied
                 SetWindowStartupLocation(owner);
+                
+                _canHandleResized = true; 
 
                 var initialSize = new Size(
                     double.IsNaN(Width) ? ClientSize.Width : Width,
@@ -1036,7 +1041,7 @@ namespace Avalonia.Controls
         /// <inheritdoc/>
         internal override void HandleResized(Size clientSize, WindowResizeReason reason)
         {
-            if (ClientSize != clientSize || double.IsNaN(Width) || double.IsNaN(Height))
+            if (_canHandleResized && (ClientSize != clientSize || double.IsNaN(Width) || double.IsNaN(Height)))
             {
                 var sizeToContent = SizeToContent;