do not discard body while error_page redirection

src/http/ngx_http_special_response.c

diff --git a/src/http/ngx_http_special_response.c b/src/http/ngx_http_special_response.c
index fd33eaf..4e045c7 100644
--- a/src/http/ngx_http_special_response.c
+++ b/src/http/ngx_http_special_response.c
@@ -327,7 +327,6 @@
 ngx_int_t
 ngx_http_special_response_handler(ngx_http_request_t *r, ngx_int_t error)
 {
-    ngx_int_t                  rc;
     ngx_uint_t                 i, err;
     ngx_http_err_page_t       *err_page;
     ngx_http_core_loc_conf_t  *clcf;
@@ -336,12 +335,6 @@
                    "http special response: %d, \"%V?%V\"",
                    error, &r->uri, &r->args);
 
-    rc = ngx_http_discard_request_body(r);
-
-    if (rc == NGX_HTTP_INTERNAL_SERVER_ERROR) {
-        error = NGX_HTTP_INTERNAL_SERVER_ERROR;
-    }
-
     r->err_status = error;
 
     if (r->keepalive) {
@@ -386,6 +379,10 @@
         }
     }
 
+    if (ngx_http_discard_request_body(r) != NGX_OK) {
+        error = NGX_HTTP_INTERNAL_SERVER_ERROR;
+    }
+
     if (clcf->msie_refresh
         && r->headers_in.msie
         && (error == NGX_HTTP_MOVED_PERMANENTLY