gunzip: fix from gzip-1.3.12 for gzip file with all zero length codes

gunzip: fix from gzip-1.3.12 for gzip file with all zero length codes

Corresponding changelog from gzip-1.3.12 reads:

"""
2006-12-20  Paul Eggert  <eggert@cs.ucla.edu>
        * inflate.c (huft_build): Fix regression that caused gzip to
        refuse to uncompress null input (all zero length codes).  Problem
        reported by Yiorgos Adamopoulos.  This regression was caused by
        the security patch installed 2006-11-20, which in turn came from
        Debian, which in turn apparently came from Thomas Biege of SuSe.
"""

function                                             old     new   delta
huft_build                                          1176    1216     +40

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>