fix segfault if there was non cached large FastCGI stderr output before header,
the bug had been introduced in r3461

src/http/modules/ngx_http_fastcgi_module.c

diff --git a/src/http/modules/ngx_http_fastcgi_module.c b/src/http/modules/ngx_http_fastcgi_module.c
index 845dd5f..b09b330 100644
--- a/src/http/modules/ngx_http_fastcgi_module.c
+++ b/src/http/modules/ngx_http_fastcgi_module.c
@@ -1254,7 +1254,7 @@
 
 #if (NGX_HTTP_CACHE)
 
-        if (f->large_stderr) {
+        if (f->large_stderr && r->cache) {
             u_char   *start;
             ssize_t   len;