SafeStr: use std::numeric_limits instead of SIZE_MAX

It's the C++ way.

Signed-off-by: Frank Lichtenheld <frank@lichtenheld.com>

openvpn/buffer/safestr.hpp

@@ -43,7 +43,7 @@ namespace openvpn {
     SafeString(const char *str, const size_t size)
       : data(size+1, BUF_FLAGS)
     {
-      if (size == SIZE_MAX)
+      if (size == std::numeric_limits<size_t>::max())
         OPENVPN_BUFFER_THROW(buffer_overflow)
       data.write((unsigned char *)str, size);
       trail();