Avoid creating wxGraphicsContext in the drawing sample unnecessarily.

This is not only wasteful, but creating a Direct2D surface associated with a
wxDC makes it impossible to paint on the DC using GDI functions, so this
completely broke the initial display in the sample.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@77690 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

samples/drawing/drawing.cpp

@@ -1550,6 +1550,8 @@ void MyCanvas::Draw(wxDC& pdc)
 #endif
         ;
 
+    if ( m_useContext )
+    {
         wxGraphicsContext* context;
         if ( wxPaintDC *paintdc = wxDynamicCast(&pdc, wxPaintDC) )
         {
@@ -1572,6 +1574,7 @@ void MyCanvas::Draw(wxDC& pdc)
         }
 
         gdc.SetGraphicsContext(context);
+    }
 
     wxDC &dc = m_useContext ? (wxDC&) gdc : (wxDC&) pdc ;
 #else