Revert "trivial" change of r61772.

The "slight code simplification" of r61772 broke the code as it could now
crash if dangling m_Cell pointer was used during parsing. Revert it and add a
comment explaining why the code is written in the way it is.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@62556 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/html/htmlwin.cpp

@@ -468,8 +468,14 @@ bool wxHtmlWindow::DoSetPage(const wxString& source)
     SetBackgroundImage(wxNullBitmap);
 
     m_Parser->SetDC(dc);
-
+    if (m_Cell)
+    {
         delete m_Cell;
+        // notice that it's important to set m_Cell to NULL here before calling
+        // Parse() below, even if it will be overwritten by its return value:
+        // without this we may crash if it's used from inside Parse()
+        m_Cell = NULL;
+    }
     m_Cell = (wxHtmlContainerCell*) m_Parser->Parse(newsrc);
     delete dc;
     m_Cell->SetIndent(m_Borders, wxHTML_INDENT_ALL, wxHTML_UNITS_PIXELS);