Implement wxProgressDialog::DoGetSize() for the native dialog too

DoGetPosition() was done in 1ef1f8fda6,
implement DoGetSize() too now in order to give a chance Centre() (which
needs both position and size to work).

See #17768.

include/wx/msw/progdlg.h

@@ -44,6 +44,7 @@ public:
     virtual void SetIcons(const wxIconBundle& icons) wxOVERRIDE;
     virtual void DoMoveWindow(int x, int y, int width, int height) wxOVERRIDE;
     virtual void DoGetPosition(int *x, int *y) const wxOVERRIDE;
+    virtual void DoGetSize(int *width, int *height) const wxOVERRIDE;
     virtual void Fit() wxOVERRIDE;
 
     virtual bool Show( bool show = true ) wxOVERRIDE;

src/msw/progdlg.cpp

@@ -838,6 +838,24 @@ void wxProgressDialog::DoGetPosition(int *x, int *y) const
     wxGenericProgressDialog::DoGetPosition(x, y);
 }
 
+void wxProgressDialog::DoGetSize(int *width, int *height) const
+{
+#ifdef wxHAS_MSW_TASKDIALOG
+    if ( HasNativeTaskDialog() )
+    {
+        const wxRect r = GetTaskDialogRect();
+        if ( width )
+            *width = r.width;
+        if ( height )
+            *height = r.height;
+
+        return;
+    }
+#endif // wxHAS_MSW_TASKDIALOG
+
+    wxGenericProgressDialog::DoGetSize(width, height);
+}
+
 void wxProgressDialog::Fit()
 {
 #ifdef wxHAS_MSW_TASKDIALOG