fix segfault when client_body_in_file_only is on, the body is not passed
to upstream, and nginx tries next upstream

src/http/ngx_http_upstream.c

diff --git a/src/http/ngx_http_upstream.c b/src/http/ngx_http_upstream.c
index 780528a..d5e6dd5 100644
--- a/src/http/ngx_http_upstream.c
+++ b/src/http/ngx_http_upstream.c
@@ -569,8 +569,11 @@
         }
     }
 
-    if (r->request_body && r->request_body->temp_file && r == r->main) {
-
+    if (r->request_body
+        && r->request_body->buf
+        && r->request_body->temp_file
+        && r == r->main)
+    {
         /*
          * the r->request_body->buf can be reused for one request only,
          * the subrequests should allocate their own temporay bufs