ads_connect: Return immediately on a failed GC connection.

ads_connect: Return immediately on a failed GC connection.

ads_connect_gc() feeds an explicit server to ads_connect().  However, if the
resulting connection fails, the latter function was attempting to find a DC
on its own and continuing the connection.  This resulting in GC searches being
sent over a connection using port 389 which would fail when using the base
search suffix outside of the domain naming context.

The fix is to fail immediately in ads_connect() since the GC lookup ordering
is handled already in ads_connect_gc().