leave HEAD method 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 4e045c7..8493268 100644
--- a/src/http/ngx_http_special_response.c
+++ b/src/http/ngx_http_special_response.c
@@ -490,8 +490,10 @@
 
     if (uri->data[0] == '/') {
 
-        r->method = NGX_HTTP_GET;
-        r->method_name = ngx_http_get_name;
+        if (r->method != NGX_HTTP_HEAD) {
+            r->method = NGX_HTTP_GET;
+            r->method_name = ngx_http_get_name;
+        }
 
         return ngx_http_internal_redirect(r, uri, args);
     }