HSI Widget indicated valid GPS fix even if SYS_STATUS indicates disabled GPS

[Susurrus]

I had my SYS_STATUS message indicate the proper invalid GPS and the GPS_RAW_INT message had a hard-coded 3D fix status and yet the HSI widget indicated a 3D GPS fix. Might it not be better to have it show the GPS as disabled whenever the corresponding SYS_STATUS field OR the GPS_RAW_INT field indicates disabled? In this case it is likely that there is a problem on the controller and it would be likely that the GPS unit or code is not working correctly.

[LorenzMeier]

Yes, that makes sense - let's take the minimum of the two - but provide good in-code documentation.