Update expectation for permessage-deflate compression result for empty payload
Update expectation for permessage-deflate compression result for empty payload

It seems newer zlib library omits unnecessary compressed block and just puts
uncompressed block for empty input.

Release note: n/a

R=yhirano@chromium.org

Review URL: https://codereview.appspot.com/179880043
googlearchive/pywebsocket,GoogleChromeLabs/pywebsocket3,google/pywebsocket,GoogleChromeLabs/pywebsocket3,google/pywebsocket,GoogleChromeLabs/pywebsocket3,googlearchive/pywebsocket,google/pywebsocket,googlearchive/pywebsocket