QUIC: fixed possible use-after-free on stream cleanup. A QUIC stream could be destroyed by handler while in ngx_quic_stream_input(). To detect this, ngx_quic_find_stream() is used to check that it still exists. Previously, a stream id was passed to this routine off the frame structure. In case of stream cleanup, it is freed along with other frames belonging to the stream on cleanup. Then, a cleanup handler reuses last frames to update MAX_STREAMS and serve other purpose. Thus, ngx_quic_find_stream() is passed a reused frame with zeroed out part pointed by stream_id. If a stream with id 0x0 still exists, this leads to use-after-free.