lttng: fix memory usage view when ust trace is in an experiment

lttng: fix memory usage view when ust trace is in an experiment

This fix avoids a TimeRangeException exception if experiment starts
before state system start time. Also, it clears the view if current
window range is outside the state system range of the memory usage.

Change-Id: I1d2afdffacfbf80db1fa90b3b2bb0c7c62d6faab
Signed-off-by: Bernd Hufmann <Bernd.Hufmann@ericsson.com>
Reviewed-on: https://git.eclipse.org/r/95125
Reviewed-by: Hudson CI
Reviewed-by: Matthew Khouzam <matthew.khouzam@ericsson.com>
Tested-by: Matthew Khouzam <matthew.khouzam@ericsson.com>
Reviewed-by: Bernd Hufmann <bernd.hufmann@ericsson.com>