Null thingholder fix

[keyz182]

Fix for issue reported by Kafungus.

Exception printing PS_PawnStatueSelfRelease5042970 at (162, 0, 151): System.ArgumentNullException: Value cannot be null.
Parameter name: source
[Ref 3AE437C8]
 at System.Linq.Enumerable.TryGetFirst[TSource] (System.Collections.Generic.IEnumerable`1[T] source, System.Boolean& found) [0x0000d] in <351e49e2a5bf4fd6beabb458ce2255f3>:0 
 at System.Linq.Enumerable.FirstOrDefault[TSource] (System.Collections.Generic.IEnumerable`1[T] source) [0x00000] in <351e49e2a5bf4fd6beabb458ce2255f3>:0 
 at PawnStorages.Building_PawnStorage.Print (Verse.SectionLayer layer) [0x0000b] in <7ccf111a7c9447fa806454de1ff42707>:0 
 at Verse.SectionLayer_ThingsGeneral.TakePrintFrom (Verse.Thing t) [0x00000] in <f0ac5eb9b52e4cc396c70fc9a4ee15e5>:0 

• Ensures the ThingHolder is actually created in the accessor.
• Sneak in a fix to trigger a redraw on rotate