Assert that a mode style *is* set, not that one isn't set.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@56381 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/generic/listctrl.cpp

@@ -5046,7 +5046,7 @@ bool wxGenericListCtrl::Create(wxWindow *parent,
     m_headerHeight = 0;
 
     // just like in other ports, an assert will fail if the user doesn't give any type style:
-    wxASSERT_MSG( !(style & wxLC_MASK_TYPE),
+    wxASSERT_MSG( (style & wxLC_MASK_TYPE),
                   _T("wxListCtrl style should have exactly one mode bit set") );
 
     if ( !wxControl::Create( parent, id, pos, size, style, validator, name ) )