We don't return rates to randr < 1.1 clients, so don't allocate space
for them.  This fixes a FatalError due to not all allocated space being
used.

X.Org bug#21861 <http://bugs.freedesktop.org/show_bug.cgi?id=21861>
Reported-by: Guillaume Quintin <coincoin169g@gmail.com>
Signed-off-by: Julien Cristau <jcristau@debian.org>