correct the inversed assert check in LVN_DELETEITEM handler (closes #10831)

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@60731 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/msw/listctrl.cpp

@@ -2222,7 +2222,7 @@ bool wxListCtrl::MSWOnNotify(int idCtrl, WXLPARAM lParam, WXLPARAM *result)
                         }
                     }
 
-                    wxASSERT_MSG( data, "invalid internal data pointer?" );
+                    wxASSERT_MSG( !data, "invalid internal data pointer?" );
                 }
                 break;