libwebsockets

make duplicate headers append instead of get ignored

The code to prevent memory leaks caused by reallocating a wsi->utf8_token
was also causing wsi->parser_state to not be updated, preventing the
handshake from completing.

This patch changes the logic to append to previous allocation which is
correct behaviour actually.

Signed-off-by: Nick Dowell <nick@nickdowell.com>
Signed-off-by: Andy Green <andy@warmcat.com>