validation: timer: don't access non-existing timers
validation: timer: don't access non-existing timers

Since e5c85d3f "validation: timer: handle early exhaustion of pool" the
workers can handle if object caches retain packets, but with enough
threads it can happen that a late starting thread won't be able to
allocate any. This for loop should take that into account and not
trying to access tt[0].ev.

Signed-off-by: Zoltan Kiss <045352d2c5c4a454a2aefff6fa815639b332fd1d@linaro.org>
Signed-off-by: Maxim Uvarov <db4d16e02ae2d7493db430203537da8b2e34f290@linaro.org>

erachmi/odp,erachmi/odp,mike-holmes-linaro/odp,nmorey/odp,dkrot/odp,erachmi/odp,ravineet-singh/odp,dkrot/odp,mike-holmes-linaro/odp,ravineet-singh/odp,nmorey/odp,ravineet-singh/odp,erachmi/odp,ravineet-singh/odp,dkrot/odp,mike-holmes-linaro/odp,nmorey/odp,nmorey/odp,dkrot/odp,mike-holmes-linaro/odp