fix r2590: error_page made an external redirect without query string

src/http/ngx_http_core_module.c

diff --git a/src/http/ngx_http_core_module.c b/src/http/ngx_http_core_module.c
index ffdd0b0..b6f4b11 100644
--- a/src/http/ngx_http_core_module.c
+++ b/src/http/ngx_http_core_module.c
@@ -3875,7 +3875,7 @@
     args.len = 0;
     args.data = NULL;
 
-    if (cv.lengths == NULL) {
+    if (cv.lengths == NULL && uri.data[0] == '/') {
         p = (u_char *) ngx_strchr(uri.data, '?');
 
         if (p) {