Use wxDELETE() and wxDELETEA() when possible.

Use wxDELETE[A]() functions which automatically NULL out their arguments after
deleting them instead of doing it manually.

Closes #9685.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@64656 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/generic/htmllbox.cpp

@@ -66,8 +66,7 @@ private:
     void InvalidateItem(size_t n)
     {
         m_items[n] = (size_t)-1;
-        delete m_cells[n];
-        m_cells[n] = NULL;
+        wxDELETE(m_cells[n]);
     }
 
 public: