Don't report distance if there is no confidence

[patrickelectric]

Right now the sensor tries to fix in any possible distance/measure, this should be avoided, the sensor should only report distance when it has the confidence that there is a real tracking point.

We may want to report distance 0 if it's invalid.

For more information:
https://discuss.bluerobotics.com/t/ping-sonar-operating-out-of-range/7903