Don't add input group during initgroups_dyn in hesiod

Don't add input group during initgroups_dyn in hesiod

Fixes BZ #15304.

The *initgroups_dyn functions are called with a group argument.  This
group gid is usually skipped while populating the grouplist since the
caller adds that group id in advance.

The hesiod initgroups_dyn implementation however adds the group gid to
the list if it does not already exist.  While it works fine for the
usual initgroups, it breaks nscd since it calls initgroups_dyn with -1
as the gid (to have all groups included).