Add missing c_str() and similar calls to samples in STL build.

Don't rely on implicit conversion of wxString to char*/wxChar*, it doesn't
exist in STL build. Add explicit c_str(), wc_str() or t_str() calls.

Closes #14420.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@71820 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

tests/benchmarks/htmlparser/htmlpars.cpp

@@ -295,7 +295,7 @@ void wx28HtmlParser::DoParsing(int begin_pos, int end_pos)
             // Add text:
             AddText(GetEntitiesParser()->Parse(
                        m_Source.Mid(pieces[m_CurTextPiece].m_pos,
-                                    pieces[m_CurTextPiece].m_lng)));
+                                    pieces[m_CurTextPiece].m_lng)).t_str());
             begin_pos = pieces[m_CurTextPiece].m_pos +
                         pieces[m_CurTextPiece].m_lng;
             m_CurTextPiece++;