Include spdy_window_update.o in OBJECTS list

spdy_ctx makes reference to spdy_proc_window_update
(spdy_ctx.c:231), so we get an unresolved reference.
Ensure version is assigned before we pack nv_block

Otherwise, the zlib environment is not configured
correctly.
Handle NULL assoc in spdy_stream_open

Otherwise we get a NP fault when opening a stream
that has no associated stream.