Fix NRE when Patched Conics are not available

Under KSP 0.90, in career mode, patched conics are only availabe after
upgrading the Tracking station. This led to a NRE referencing patched
conics.

Thanks to Cydonian Monk for this patch.
Notify user when activating trajectories without patched Conics

Disable Trajectory display if patched conics are not available in the
Tracking Station.