Reject trailing Brotli data to prevent infinite drain loops

[illia-v]

Reject trailing data after a complete stream, matching error check of the reference Brotli. This prevents infinite loops while draining the decoder.

Reproducer:

import brotlicffi as brotli  # or import brotli

data = brotli.compress(b"A" * (2**21)) + b"tail"
decoder = brotli.Decompressor()
decoder.process(data, output_buffer_limit=2**20)

while not decoder.can_accept_more_data():
    decoder.process(b"", output_buffer_limit=2**20)

Unpatched brotlicffi loops indefinitely. Patched brotlicffi and reference Brotli raise an error.