return NGX_HTTP_UPSTREAM_INVALID_HEADER for invalid status

src/http/modules/ngx_http_fastcgi_module.c

diff --git a/src/http/modules/ngx_http_fastcgi_module.c b/src/http/modules/ngx_http_fastcgi_module.c
index 5a15fc1..7b799c5 100644
--- a/src/http/modules/ngx_http_fastcgi_module.c
+++ b/src/http/modules/ngx_http_fastcgi_module.c
@@ -1174,7 +1174,10 @@
                     status = ngx_atoi(status_line->data, 3);
 
                     if (status == NGX_ERROR) {
-                        return NGX_HTTP_INTERNAL_SERVER_ERROR;
+                        ngx_log_error(NGX_LOG_ERR, r->connection->log, 0,
+                                      "upstream sent invalid status \"%V\"",
+                                      status_line);
+                        return NGX_HTTP_UPSTREAM_INVALID_HEADER;
                     }
 
                     u->headers_in.status_n = status;