Fixed fastcgi_pass with UNIX socket and variables (ticket #855).

This was broken in a93345ee8f52 (1.9.8).

src/http/ngx_http_upstream.c

diff --git a/src/http/ngx_http_upstream.c b/src/http/ngx_http_upstream.c
index 78f6e34..6c6ee80 100644
--- a/src/http/ngx_http_upstream.c
+++ b/src/http/ngx_http_upstream.c
@@ -642,7 +642,9 @@
 
         if (u->resolved->sockaddr) {
 
-            if (u->resolved->port == 0) {
+            if (u->resolved->port == 0
+                && u->resolved->sockaddr->sa_family != AF_UNIX)
+            {
                 ngx_log_error(NGX_LOG_ERR, r->connection->log, 0,
                               "no port in upstream \"%V\"", host);
                 ngx_http_upstream_finalize_request(r, u,