In the upstream google/brotli, if the `decompress` function receives an empty byte
string, it returns a brotli.error; whereas in 'brotlipy' it does not raise but
returns an empty string b"":
https://github.com/python-hyper/brotlipy/issues/43#issuecomment-240378257
This test case asserts that when 'totalCompressedSize' in the WOFF2 header is
incorrectly set, the woff2 reader fails -- either because the brotli decoder
raises an exception, or it returns a string whose length is not the one expected.
855c3b17c9