Don't check multiple in-sequence NULL in spdylay_frame_count_unpack_nv_space

If we return negative error code in that function, it means frame will not
unpacked and ends up to lose any information the frame contains.
The spec says it should send RST_STREAM with PROTOCOL_ERROR, so we need
at least stream ID.
Therefore, the check should be performed in
spdylay_session_on_syn_stream_received().

lib/spdylay_frame.c

@@ -118,11 +118,6 @@ int spdylay_frame_count_unpack_nv_space
     }
     for(off -= len, j = off+len; off != j; ++off) {
       if(in[off] == '\0') {
-        /* spdy/2 spec says it does not allow multiple, in-sequence
-           NULL characters */
-        if(off+1 != j && in[off+1] == '\0') {
-          return SPDYLAY_ERR_INVALID_ARGUMENT;
-        }
         ++nvlen;
       }
     }