SPDY: fixed connection leak while waiting for request headers.

SPDY: fixed connection leak while waiting for request headers.

If an error occurs in a SPDY connection, the c->error flag is set on every fake
request connection, and its read or write event handler is called, in order to
finalize it.  But while waiting for request headers, it was a no-op since the
read event handler had been set to ngx_http_empty_handler().