datastore: Fast return to for classic node children

datastore: Fast return to for classic node children

When selecting next children of classic nodes, once the node's
end time is past the maximum of the range, it is no use searching
the rest of the children.

Change-Id: I7a1aba410718ea33a84b6a0b109121b0512fd284
Signed-off-by: Geneviève Bastien <gbastien+lttng@versatic.net>
Reviewed-on: https://git.eclipse.org/r/91758
Reviewed-by: Hudson CI
Reviewed-by: Loic Prieur-Drevon <loic.prieur.drevon@ericsson.com>