SPDY: fixed check for too long header name or value.

For further progress a new buffer must be at least two bytes larger than
the remaining unparsed data.  One more byte is needed for null-termination
and another one for further progress.  Otherwise inflate() fails with
Z_BUF_ERROR.

src/http/ngx_http_spdy.c

diff --git a/src/http/ngx_http_spdy.c b/src/http/ngx_http_spdy.c
index ae95efd..9cac691 100644
--- a/src/http/ngx_http_spdy.c
+++ b/src/http/ngx_http_spdy.c
@@ -2660,10 +2660,10 @@
     rest = r->header_in->last - r->header_in->pos;
 
     /*
-     * equality is prohibited since one more byte is needed
-     * for null-termination
+     * One more byte is needed for null-termination
+     * and another one for further progress.
      */
-    if (rest >= cscf->large_client_header_buffers.size) {
+    if (rest > cscf->large_client_header_buffers.size - 2) {
         p = r->header_in->pos;
 
         if (rest > NGX_MAX_ERROR_STR - 300) {