HTTP/2: fixed segfault on DATA frames after 400 errors. If 400 errors were redirected to an upstream server using the error_page directive, DATA frames from the client might cause segmentation fault due to null pointer dereference. The bug had appeared in 6989:2c4dbcd6f2e4 (1.13.0). Fix is to skip such frames in ngx_http_v2_state_read_data() (similarly to 7561:9f1f9d6e056a). With the fix, behaviour of 400 errors in HTTP/2 is now similar to one in HTTP/1.x, that is, nginx doesn't try to read the request body. Note that proxying 400 errors, as well as other early stage errors, to upstream servers might not be a good idea anyway. These errors imply that reading and processing of the request (and the request headers) wasn't complete, and proxying of such incomplete request might lead to various errors. Reported by Chenglong Zhang.

scgi_param  REQUEST_METHOD     $request_method;
scgi_param  REQUEST_URI        $request_uri;
scgi_param  QUERY_STRING       $query_string;
scgi_param  CONTENT_TYPE       $content_type;

scgi_param  DOCUMENT_URI       $document_uri;
scgi_param  DOCUMENT_ROOT      $document_root;
scgi_param  SCGI               1;
scgi_param  SERVER_PROTOCOL    $server_protocol;
scgi_param  REQUEST_SCHEME     $scheme;
scgi_param  HTTPS              $https if_not_empty;

scgi_param  REMOTE_ADDR        $remote_addr;
scgi_param  REMOTE_PORT        $remote_port;
scgi_param  SERVER_PORT        $server_port;
scgi_param  SERVER_NAME        $server_name;