Fixing Z_BUF_ERROR when no content

[lejahmie]

When response headers content-encoding is set but no content exist zlib fails with Z_BUF_ERROR.

Solution is to check if data exist, if it does not we should never try to decompress.
If no data exists, but content-encoding still says it is encoded we simply remove the header not confuse downstream operations.

Fixes:
#3989
#3648
#3055

[lejahmie]

Fixed issues with eslint tests

[jasonsaayman]

Thanks this looks good 😊

[lejahmie]

@jasonsaayman you can probably close these when this is in;
#3989
#3648
#3055

[jasonsaayman]

Thanks will do