www/{nginx,nginx-devel,freenginx}: 3rd-party modules management

Fix three defects in the body filter of the zstd module. A worker spins
at 100% CPU forever when an empty flush buffer arrives and the compressor
has nothing left to flush. A response is truncated at 131072 bytes when
a single input buffer larger than that carries last_buf. An output
buffer that is already full when ZSTD_endStream() is due gets dropped.

Upstream has not taken a code change since April 2024.

PR: 299100
Sponsored by: Netzkommune GmbH