fix r2378, do not activate subrequest if there are already
postponed subrequests or data

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 6a72f31..458e456 100644
--- a/src/http/ngx_http_core_module.c
+++ b/src/http/ngx_http_core_module.c
@@ -2094,9 +2094,18 @@
     sr->write_event_handler = ngx_http_handler;
 
     if (c->data == r) {
+
+        for (pr = r->postponed; pr; pr = pr->next) {
+            if (pr->request) {
+                goto no_activate;
+            }
+        }
+
         c->data = sr;
     }
 
+no_activate:
+
     sr->in_addr = r->in_addr;
     sr->port = r->port;
     sr->port_text = r->port_text;