Flush buffer to avoid deleting data when seeking NoopStream

[nhz2]

This fixes one of the broken tests.

This also matches the pattern in unsafe_write where flushbuffer is called before the position in the underlying stream is adjusted if the stream is in :write mode.

TranscodingStreams.jl/src/noop.jl

Lines 106 to 117 in db9b0ed

	function Base.unsafe_write(stream::NoopStream, input::Ptr{UInt8}, nbytes::UInt)
	changemode!(stream, :write)
	buffer = stream.buffer1
	if marginsize(buffer) ≥ nbytes
	copydata!(buffer, input, nbytes)
	return Int(nbytes)
	else
	flushbuffer(stream)
	# directly write data to the underlying stream
	return unsafe_write(stream.stream, input, nbytes)
	end
	end