The assert only evaluates to code if NDEBUG is undefined. Protect rv and its use accordingly

Issue reported by Joerg Mayer
https://code.wireshark.org/review/8260

This reverts commit 7bb154f7.

Use static pattern rules to use same recipe for nghttpx-init and
nghttpx.service.

Also rewrite how to produce nghttpx

This is a regression introduced in
4be4d875

Merge branch 'patch-systemd-service' of https://github.com/wzyboy/nghttp2 into wzyboy-patch-systemd-service

- Avoid changing file permissions
- Make sure all log files are reopened
- Remove non-sense prerotate script
- Send SIGUSR1 to all nghttpx processes

Merge branch 'include_pull_request' of https://github.com/alex-nalivko/nghttp2 into alex-nalivko-include_pull_request

Merge branch 'finer_stats' of https://github.com/ericcarlschwartz/nghttp2 into ericcarlschwartz-finer_stats

finer statistics for h2load: update per comments from tatsuhiro-t

finer stats for h2load: fixed formatting