fix segfault introduced in r2845

src/http/ngx_http_variables.c

diff --git a/src/http/ngx_http_variables.c b/src/http/ngx_http_variables.c
index 28c82ef..d41b996 100644
--- a/src/http/ngx_http_variables.c
+++ b/src/http/ngx_http_variables.c
@@ -1492,7 +1492,10 @@
     ngx_buf_t    *buf, *next;
     ngx_chain_t  *cl;
 
-    if (r->request_body == NULL || r->request_body->temp_file) {
+    if (r->request_body == NULL
+        || r->request_body->bufs == NULL
+        || r->request_body->temp_file)
+    {
         v->not_found = 1;
 
         return NGX_OK;