NIF controllers from sheath meshes are used

If you copy-paste the whole bow mesh to the sheath mesh without removing morph controllers, you may get a situation where when shooting animation will be played both in NifSkope and in-game when the bow is sheathed. The issue is reproducable with bows from this mod (at least with chitin and daedric ones).

To avoid such situaton, we already assign NullAnimationTime source for fallback situation when we do not have an _sh mesh and use a weapon mesh instead, but we forgot about the case when someone would place keyframe or morph controller to manually created _sh mesh.