QUIC: fixed ngx_http_test_reading() for QUIC streams. Previously this function generated an error trying to figure out if client shut down the write end of the connection. The reason for this error was that a QUIC stream has no socket descriptor. However checking for eof is not the right thing to do for an HTTP/3 QUIC stream since HTTP/3 clients are expected to shut down the write end of the stream after sending the request. Now the function handles QUIC streams separately. It checks if c->read->error is set. The error flags for c->read and c->write are now set for all streams when closing the QUIC connection instead of setting the pending_eof flag.