Do a sanity check to make sure GetWindow() has a valid window, and assert if it doesn't. On OS X Cocoa, try to continue on in release mode.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@58797 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/osx/carbon/graphics.cpp

@@ -2435,11 +2435,14 @@ wxGraphicsContext * wxMacCoreGraphicsRenderer::CreateContext( const wxWindowDC&
         int w, h;
         win_impl->GetSize( &w, &h );
         CGContextRef cgctx = 0;
-#ifdef __WXMAC__
+        wxASSERT_MSG(win_impl->GetWindow(), "Invalid wxWindow in wxMacCoreGraphicsRenderer::CreateContext");
+        if (win_impl->GetWindow())
             cgctx =  (CGContextRef)(win_impl->GetWindow()->MacGetCGContextRef());
-#else
+#if wxOSX_USE_COCOA
+        else
             cgctx = wxMacGetContextFromCurrentNSContext() ;
 #endif
+        if (cgctx != 0)
             return new wxMacCoreGraphicsContext( this, cgctx, (wxDouble) w, (wxDouble) h );
     }
     return NULL;