Use wxString::t_str() in calls to Windows API functions in wxMSW.

Use t_str() instead of wx_str() to make the code work correctly in UTF-8 build
in which wx_str() returns a pointer to UTF-8 buffer while we need a wchar_t
pointer for Windows.

Closes #14371.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@71640 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/msw/radiobox.cpp

@@ -203,7 +203,7 @@ bool wxRadioBox::Create(wxWindow *parent,
         wxWindowIDRef subid = NewControlId();
 
         HWND hwndBtn = ::CreateWindow(wxT("BUTTON"),
-                                      choices[i].wx_str(),
+                                      choices[i].t_str(),
                                       styleBtn,
                                       0, 0, 0, 0,   // will be set in SetSize()
                                       GetHwndOf(parent),