alpn: allow NULL alpn in role struct when scanning for match
alpn: allow NULL alpn in role struct when scanning for match

https://github.com/warmcat/libwebsockets/issues/1262
sartura/libwebsockets,sartura/libwebsockets,sartura/libwebsockets,sartura/libwebsockets,sartura/libwebsockets,sartura/libwebsockets,sartura/libwebsockets