SPDY: fixed possible uninitialized memory access.

The frame->stream pointer should always be initialized for control frames since
the check against it can be performed in ngx_http_spdy_filter_cleanup().

src/http/ngx_http_spdy.c

diff --git a/src/http/ngx_http_spdy.c b/src/http/ngx_http_spdy.c
index e576196..01b8e28 100644
--- a/src/http/ngx_http_spdy.c
+++ b/src/http/ngx_http_spdy.c
@@ -1633,8 +1633,8 @@
     frame->first = cl;
     frame->last = cl;
     frame->handler = ngx_http_spdy_settings_frame_handler;
-#if (NGX_DEBUG)
     frame->stream = NULL;
+#if (NGX_DEBUG)
     frame->size = NGX_SPDY_FRAME_HEADER_SIZE
                   + NGX_SPDY_SETTINGS_NUM_SIZE
                   + NGX_SPDY_SETTINGS_PAIR_SIZE;
@@ -1722,6 +1722,7 @@
         frame->first = cl;
         frame->last = cl;
         frame->handler = ngx_http_spdy_ctl_frame_handler;
+        frame->stream = NULL;
     }
 
     frame->free = NULL;
@@ -1733,7 +1734,6 @@
         return NULL;
     }
 
-    frame->stream = NULL;
     frame->size = size;
 #endif