HTTP/2: fixed segfault when memory allocation failed. If allocation of cleanup handler in the HTTP/2 header filter failed, then a stream might be freed with a HEADERS frame left in the output queue. Now the HEADERS frame is accounted in the queue before trying to allocate the cleanup handler.

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


have=NGX_SUPPRESS_WARN . auto/have

have=NGX_SMP . auto/have