TMF: Fix IndexOutOfBoundException when querying state system

TMF: Fix IndexOutOfBoundException when querying state system

Fixes bug 432191 where the size of the stateInfo array may be smaller than
the ongoingStateInfo when the method is called. We use the size we know is the
smallest to avoid this exception to be thrown.

Change-Id: I1494940726b952ffe94560a7bed6e5764ff3d8f9
Signed-off-by: Geneviève Bastien <gbastien+lttng@versatic.net>
Reviewed-on: https://git.eclipse.org/r/24661
Reviewed-by: Alexandre Montplaisir <alexmonthy@voxpopuli.im>
Tested-by: Hudson CI