HTTP/3: fixed parsing encoder insertions with empty header value. When starting processing a new encoder instruction, the header state is not memzero'ed because generally it's burdensome. If the header value is empty, this resulted in inserting a stale value left from the previous instruction. Based on a patch by Zhiyong Sun.

# Copyright (C) Igor Sysoev
# Copyright (C) Nginx, Inc.


cat << END >> $NGX_AUTO_CONFIG_H

#ifndef $have
#define $have  0
#endif

END