The orbit analyser throws exceptions in some situations where the orbit is not gravitationally bound

[eggrobin]

Reported by @al2me6 with the C# stack below. It sounds like the primary is null, and that this breaks the celestial strings; probably introduced in either Haar (with celestial strings) or Hamilton (with the localization cache).

[EXC 15:04:45.373] ArgumentNullException: Value cannot be null.
Parameter name: key
    System.Collections.Generic.Dictionary`2[TKey,TValue].FindEntry (TKey key) (at <ad04dee02e7e4a85a1299c7ee81c79f6>:0)
    System.Collections.Generic.Dictionary`2[TKey,TValue].TryGetValue (TKey key, TValue& value) (at <ad04dee02e7e4a85a1299c7ee81c79f6>:0)
    principia.ksp_plugin_adapter.L10N.Name (CelestialBody body) (at <65c7bf2f4e324461b01170ebbad8bf3b>:0)
    principia.ksp_plugin_adapter.L10N+<>c.<CelestialString>b__15_0 (CelestialBody body) (at <65c7bf2f4e324461b01170ebbad8bf3b>:0)
    System.Linq.Enumerable+<SelectManyIterator>d__167`3[TSource,TCollection,TResult].MoveNext () (at <fbb5ed17eb6e46c680000f8910ebb50c>:0)
    System.Collections.Generic.LargeArrayBuilder`1[T].AddRange (System.Collections.Generic.IEnumerable`1[T] items) (at <fbb5ed17eb6e46c680000f8910ebb50c>:0)
    System.Collections.Generic.SparseArrayBuilder`1[T].AddRange (System.Collections.Generic.IEnumerable`1[T] items) (at <fbb5ed17eb6e46c680000f8910ebb50c>:0)
    System.Collections.Generic.SparseArrayBuilder`1[T].ReserveOrAdd (System.Collections.Generic.IEnumerable`1[T] items) (at <fbb5ed17eb6e46c680000f8910ebb50c>:0)
    System.Linq.Enumerable+Concat2Iterator`1[TSource].ToArray () (at <fbb5ed17eb6e46c680000f8910ebb50c>:0)
    System.Linq.Enumerable.ToArray[TSource] (System.Collections.Generic.IEnumerable`1[T] source) (at <fbb5ed17eb6e46c680000f8910ebb50c>:0)
    principia.ksp_plugin_adapter.L10N.CelestialString (System.String template, CelestialBody[] bodies, System.Object[] args) (at <65c7bf2f4e324461b01170ebbad8bf3b>:0)
    principia.ksp_plugin_adapter.OrbitAnalyser.RenderOrbitalElements (System.Nullable`1[T] elements, CelestialBody primary) (at <65c7bf2f4e324461b01170ebbad8bf3b>:0)
    principia.ksp_plugin_adapter.OrbitAnalyser.RenderWindow (System.Int32 window_id) (at <65c7bf2f4e324461b01170ebbad8bf3b>:0)
    principia.ksp_plugin_adapter.BaseWindowRenderer.RenderWindowAndRecordTooltip (System.Int32 window_id) (at <65c7bf2f4e324461b01170ebbad8bf3b>:0)
    UnityEngine.GUILayout+LayoutedWindow.DoWindow (System.Int32 windowID) (at <fa6f9762ac624af092525d37c9d516c4>:0)
    UnityEngine.GUI.CallWindowDelegate (UnityEngine.GUI+WindowFunction func, System.Int32 id, System.Int32 instanceID, UnityEngine.GUISkin _skin, System.Int32 forceRect, System.Single width, System.Single height, UnityEngine.GUIStyle style) (at <fa6f9762ac624af092525d37c9d516c4>:0)
    UnityEngine.DebugLogHandler:LogException(Exception, Object)
    ModuleManager.UnityLogHandle.InterceptLogHandler:LogException(Exception, Object)
    UnityEngine.Debug:CallOverridenDebugHandler(Exception, Object)