[v5] Quickfix for devision by 0 in updateLocationQualityMap

In some cases the normalized quality is NaN. Then, the json (application
state) can not be decoded and everything fails:
INF avgRttNormalized := (rtt - minAvgRtt) / (maxAvgRtt - minAvgRtt)
INF avgRttNormalized := (126 - 126) / (126 - 126) => NaN
This will be fixed in a nice way in the future when we decided more
about gateway selection (and mybe have a quality given by menshen)