Upstream: fixed non-buffered proxying with eventport.

For new data to be reported with eventport on Solaris,
ngx_handle_read_event() needs to be called after reading response
headers.  To do so, ngx_http_upstream_process_non_buffered_upstream()
now called unconditionally if there are no prepread data.  This
won't cause any read() syscalls as long as upstream connection
is not ready for reading (c->read->ready is not set), but will result
in proper handling of all events.

src/http/ngx_http_upstream.c

diff --git a/src/http/ngx_http_upstream.c b/src/http/ngx_http_upstream.c
index 9cbb5a3..a01784a 100644
--- a/src/http/ngx_http_upstream.c
+++ b/src/http/ngx_http_upstream.c
@@ -3011,9 +3011,7 @@
                 return;
             }
 
-            if (u->peer.connection->read->ready || u->length == 0) {
-                ngx_http_upstream_process_non_buffered_upstream(r, u);
-            }
+            ngx_http_upstream_process_non_buffered_upstream(r, u);
         }
 
         return;