Access log: fix "request_length" format length

The variable handler uses "%O" format specifier.

Reported by Mufeed VH of Winfunc Research.

src/http/modules/ngx_http_log_module.c

@@ -243,7 +243,7 @@ static ngx_http_log_var_t  ngx_http_log_vars[] = {
     { ngx_string("bytes_sent"), NGX_OFF_T_LEN, ngx_http_log_bytes_sent },
     { ngx_string("body_bytes_sent"), NGX_OFF_T_LEN,
                           ngx_http_log_body_bytes_sent },
-    { ngx_string("request_length"), NGX_SIZE_T_LEN,
+    { ngx_string("request_length"), NGX_OFF_T_LEN,
                           ngx_http_log_request_length },
 
     { ngx_null_string, 0, NULL }