Tuner HAL VTS: LnbLive Test Fix

This CL checks to see if the frontends given in the LnbLive dataflow are
accompanied by a software frontend. If so, these tests are not ran,
because this does not model a real world use case that would be
intentionally configured by a vendor.

Furthermore, the implemented code fixes a bug that would cause the VTS
to crash if the LnbLive tests were ran using a software frontend without
the vendor having configred the Live dataflow. Previously, the
workaround for using a software frontend with an Lnb was to use the dvr
source configured in the live dataflow to simulate input to the frontend.
Now that vendors do not need to provide this in their configuration file
(because it will be automatically generated for them), this access causes
an error that makes the VTS crash. With this new fix, this logic will never be
exectuted, and the VTS will not crash in this case.

Bug: b/240305035

Test: Test: vts-tradefed run vts --module VtsHalTvTunerTargetTest.
Change-Id: I68dc7ff4cfd103a51e3e8d7c6ff787d349a9e241