Interpret value of -1 from decawave anchor as invalid and calculate measurment update accordingly.

[kleinma]

Made it so noise is increased to 1e20. However, there is a bug where all the values go to NaN or Inf. And this may be the cause https://github.com/cwrucutter/snowmower_localization/blob/1c1ea38bc43369e5d111ad427bd2c815abcef81c/src/ekf.cpp#L316-L327