Probes still connect through unpowered relay

[liamdennehy]

So GPP's Thalia is really hot. Not knowing that I still sent two relays ahead of my probe fleet, but one burnt up its' relay antennas in orbit and the other burned up its' solar panels. With only an hour left of power the second still relayed the science data that could be gleaned as another probe entered the SOI.

Staying in the Space Center scene, I watched the relay sat's battery drain, but reaching zero and going offline did not interrupt the other probe's status. Switching to the probe it is still controllable with a strong signal, though science transmission is reduced to 0.1B/s (from over 1KB/s).

Actual behaviour Relay satellite's batteries going dead does not affect dependent probes (except perhaps greatly reduced science transmission rates).

Expected behaviour When a relay satellite's batteries go dead, the probes relaying through should be unreachable and science transmission stopped unless another relay is available

[gotmachine]

Maybe related to #674 I guess something has changed regarding CommNet background processing in recent KSP versions.