body_filter_by_lua case some strange behaviors

[9268]

中文讨论：https://groups.google.com/g/openresty/c/kCQM3WcLC-k/m/xPckMVBSBwAJ

by using body_filter_by_lua with ngx.arg[1] uncahange，it return strange truncated response add chunked_transfer_encoding off ,it return duplicate response line #file-zcurl-filterandchunkoff-out-L97 && #file-zcurl-filterandchunkoff-out-L142

i test it on latest openresty 1.21.4.1 and Tengine/2.3.2(nginx/1.17.3) , Tengine is all ok

see full conf and debug log here: https://gist.github.com/9268/a9491787efa50201fbc48d82e5de1406

if someone can provide some test case example ，i can write some cases