Fix station bug for empty InstrumentSensitivity responses.

[junghao]

As described in https://github.com/GeoNet/tickets/issues/14280.

Station SMHS LFF has empty InstrumentSensitivity data. This code makes the field output empty like this:

#Network | Station | Location | Channel | Latitude | Longitude | Elevation | Depth | Azimuth | Dip | SensorDescription | Scale | ScaleFreq | ScaleUnits | SampleRate | StartTime | EndTime
NZ|SMHS|50|LFF|-43.262160|172.334630|181.000000|0.000000|0.000000|0.000000|Fluxgate Magnetometer||||1.000000|2012-10-16T04:30:00|2013-01-15T11:00:00
NZ|SMHS|50|LFF|-43.262160|172.334630|181.000000|0.000000|0.000000|0.000000|Fluxgate Magnetometer||||1.000000|2013-01-16T00:30:00|2013-04-18T00:00:00
NZ|SMHS|50|LFF|-43.262160|172.334630|181.000000|0.000000|0.000000|0.000000|Fluxgate Magnetometer||||1.000000|2013-04-18T00:10:00|2014-10-14T00:00:00
NZ|SMHS|50|LFF|-43.262160|172.334630|181.000000|0.000000|0.000000|0.000000|Fluxgate Magnetometer||||1.000000|2014-10-14T00:00:05|

[CallumNZ]

LGTM