[ccache] ccache doesn't notice gzip CRC errors

[Wilson Snyder]

>> GZIP files contain CRC checksums, however ccache doesn't
>> notice CRC errors because it doesn't check gzerror at the
>> end of decompression.  This patch fixes it.  (It's arguably
>> a bad API decision on the gz library's part, but we're stuck
>> with it.)
>...
>
>> +	gzeof(gz_in);
>
>Why is the above gzeof call needed? The implementation doesn't seem to
>modify the state and the documentation doesn't imply that it could.

You're right, that was left from my debugging; remove it.

>Looks good otherwise.

Thanks.

-Wilson