blockContent with body size much bigger than matcher buffer returns 500

[szuecs]

Describe the bug

a bit similar to #2605

To Reproduce

% ./bin/skipper -inline-routes='r: * -> status(200) -> inlineContent("OK") -> <shunt>' -address :9001 &
[APP]ERRO[0007] error while discarding remainder request body: unexpected EOF.
127.0.0.1 - - [06/Oct/2023:11:13:07 +0200] "POST /foo HTTP/1.1" 499 2 "-" "curl/7.49.0" 1 127.0.0.1:9001 - -

% ./bin/skipper -max-matcher-buffer-size 100 -inline-routes='r: * -> blockContent("request") -> "http://127.0.0.1:9001";' &
[APP]ERRO[0005] error while proxying after 1.687247ms, route r with backend network http://127.0.0.1:9001, status code 500: dialing failed false: unexpected error from Go stdlib net/http package during roundtrip: net/http: HTTP/1.x transport connection broken: http: ContentLength=100003 with Body length 0, remote host: 127.0.0.1, request: "POST /foo HTTP/1.1", host: 127.0.0.1:9090, user agent: "curl/7.49.0"

% curl -d $(ruby -e 'print ("A"*100000)+"ret"') http://127.0.0.1:9090/foo
Internal Server Error

Expected behavior

Client should get the 200 OK instead

Observed behavior

Client got 500 Internal Server Error

[szuecs]

After #2828 I can not reproduce it anymore. Doubling the input returns zsh: argument list too long: curl