Poses do not intially show up in pose tab in Persona

The pose asset list does not update unless Persona is closed and opened or if the user searches in the search bar.

This is a regression from 4.13.2

Same thing as this old bug: https://jira.it.epicgames.net/browse/UE-32576

1. Launch QAGame in editor.
2. Create a new Pose Asset based on UE4_Mannequin_Skeleton.
3. Open the pose asset in editor.
4. In the Anim Details Panel, click the dropdown for Source Animation and Select ThirdPersonRun.
5. Click Update Source.

Result: The pose asset list isn't updated.