Failure to capture image whilst not connected to network fails to restart

[leighghunt]

If camera is both offline, and image fails to capture, logic in saveTelemetry.py - scheduleShutdown fails to cause restart.

This condition isn't true as secondsSinceLastImageCapture is -1.

# Most recent image captured (may also be in uploaded folder) is older than 10 minutes
                        if secondsSinceLastImageCapture > 600 and secondsSinceLastUpload > 600:
                            logger.warning('Most recent captured image is ' + str(secondsSinceLastImageCapture) + 'seconds old, and uploaded image is ' + str(secondsSinceLastUpload) + ' seconds old - restarting...')
                            triggerRestart = True