SensorType: return invalid data when converting invalid sensor types

These are known sensor types, that have no valid assigned value. Hence cannot be converted. Use an invalid float value. For int there is not invalid int value. In dsm-api, the sensor value is limited to 8-bit, hence using INT_MIN since that exceeds that value. #14861

Signed-off-by: Andreas Fenkart andreas.fenkart@dev.digitalstrom.org