Fix wxRegion::Offset() copy on write behaviour in wxMSW.

Offset the correct, new and unshared, region handle instead of the old and
possibly shared one.

Closes #15690.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@75251 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/msw/region.cpp

@@ -164,8 +164,7 @@ void wxRegion::Clear()
 
 bool wxRegion::DoOffset(wxCoord x, wxCoord y)
 {
-    const HRGN hrgn = GetHrgn();
-    wxCHECK_MSG( hrgn, false, wxT("invalid wxRegion") );
+    wxCHECK_MSG( GetHrgn(), false, wxT("invalid wxRegion") );
 
     if ( !x && !y )
     {
@@ -175,7 +174,7 @@ bool wxRegion::DoOffset(wxCoord x, wxCoord y)
 
     AllocExclusive();
 
-    if ( ::OffsetRgn(hrgn, x, y) == ERROR )
+    if ( ::OffsetRgn(GetHrgn(), x, y) == ERROR )
     {
         wxLogLastError(wxT("OffsetRgn"));