TMF: Check if state system is available before scheduling analysis

TMF: Check if state system is available before scheduling analysis

Adding tracing capabilities to analyses shows that an analysis is scheduled
a LOT of times just to get the state system. We should check the state system
is not null before scheduling.

Change-Id: Ic5b159566b0b84211e1b9506f4d0ecfa08df0dc6
Signed-off-by: Geneviève Bastien <gbastien+lttng@versatic.net>
Reviewed-on: https://git.eclipse.org/r/38271
Reviewed-by: Hudson CI
Reviewed-by: Bernd Hufmann <bernd.hufmann@ericsson.com>
Tested-by: Bernd Hufmann <bernd.hufmann@ericsson.com>