(Port to 2.8) Fix for wxMemoryDC::GetAsBitmap(wxRect) on Windows.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/branches/WX_2_8_BRANCH@48236 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/msw/dcmemory.h

@@ -28,6 +28,9 @@ protected:
     virtual void DoGetSize(int* width, int* height) const;
     virtual void DoSelect(const wxBitmap& bitmap);
 
+    virtual wxBitmap DoGetAsBitmap(const wxRect* subrect) const 
+    { return subrect == NULL ? GetSelectedBitmap() : GetSelectedBitmap().GetSubBitmapOfHDC(*subrect, GetHDC() );}
+
     // create DC compatible with the given one or screen if dc == NULL
     bool CreateCompatible(wxDC *dc);