issue with FamilyLocal ie AF_UNIX and local accounts

[Alban Browaeys]

This affect gnome-initial-setup  program that fails with "no protocol
specified".

I can reproduce with "DISPLAY=:0 xhost" from a root console (with xorg
session setup to allow si:localuser:<root&gdm&gnome-intial-setup> as
exhibited by the same  xhost command  run with 2566835b reverted from
xserver .

Best,
Alban

Bug report:
https://bugs.freedesktop.org/show_bug.cgi?id=86865

ie family local go through the validhosts checks

xserver returns early in ClientAuthorized > InvalidHost without checking
via get_pwnam after the 2566835b commit (Eliminate uninitialized value
warnings from access.c) . This is with FamilyLocal , ConvertAddress
returns immediatly thus addr is kept null (family is set to 256. Then
the commit that eliminate uninitialized value went too far as to check
for addr null before siAddrMatch .

siAddrMatch called into get_pwname before this commit via
siLocalCredAddrMatch then siLocalCredGetId.

This breaks gdm initial setup (gnoem-continuous which is at
1.16.99.901 . Tested against master too .

The attached patch removed the check for null an addr before siAddrMatch
and addrEqual (the latter for consistency as in the same context ).