Remove unneccessary check from ws_connbuf_append

In some cases, you want to append 0 bytes to unblock the buffer
Fix typo in serializer header
Merge pull request #227 from matthiasbeyer/fix-serializer

Fix typo in serializer header
Merge pull request #226 from neithernut/fix-ws_connbuf_append

Remove unneccessary check from ws_connbuf_append