Pose Library: explicitly call `pose_action.asset_generate_preview()`

Explicitly call `ID.asset_generate_preview()` after marking the pose as
asset. This is required since rB1c5722ba071a

pose_library/pose_creation.py

@@ -316,6 +316,7 @@ def create_pose_asset(
         return None
 
     pose_action.asset_mark()
+    pose_action.asset_generate_preview()
     return pose_action