Fix broken PSID problem on cygheap in account handling

* pwdgrp.h: Add comment to explain below change.
        (struct pg_pwd): Convert sid member to BYTE array.
        (struct pg_grp): Ditto.
        * grp.cc (pwdgrp::parse_group): Accommodate above change.
        * passwd.cc (pwdgrp::parse_passwd): Ditto.

Signed-off-by: Corinna Vinschen <corinna@vinschen.de>

winsup/cygwin/grp.cc

@@ -47,7 +47,9 @@ pwdgrp::parse_group ()
     return false;
   /* Don't generate gr_mem entries. */
   grp.g.gr_mem = &null_ptr;
-  grp.sid.getfromgr_passwd (&grp.g);
+  cygsid csid;
+  csid.getfromgr_passwd (&grp.g);
+  RtlCopySid (SECURITY_MAX_SID_SIZE, grp.sid, csid);
   return true;
 }