zlib: fix decompression of empty data streams

add4b0ab made the assumption that compressed data
would never lead to an empty decompressed stream.

Fix that by explicitly checking the number of read bytes.

PR-URL: https://github.com/nodejs/node/pull/17042
Fixes: https://github.com/nodejs/node/issues/17041
Refs: https://github.com/nodejs/node/pull/13322


Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Evan Lucas <evanlucas@me.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>