don't use implicit wxString->char*/wchar_t* conversion, it will not be available in wxUSE_STL build in the future

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@46391 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/common/tarstrm.cpp

@@ -829,8 +829,8 @@ wxTarNumber wxTarInputStream::GetHeaderNumber(int id) const
 
     if ((value = GetExtendedHeader(m_hdr->Name(id))) != wxEmptyString) {
         wxTarNumber n = 0;
-        const wxChar *p = value;
-        while (*p == ' ')
+        wxString::const_iterator p = value.begin();
+        while (*p == ' ' && p != value.end())
             p++;
         while (isdigit(*p))
             n = n * 10 + (*p++ - '0');