Thresholds are no longer automatically calculated after deleting Motion fields in Blendtrees

Steps to reproduce:

1. Open any Project
2. Create an Animator and open it
3. Create a Blendtree and double click it
4. Select the Parent Blendtree State
5. In the Inspector click the "+" icon near the Motion list and add a Motion
6. Now make sure "Automate Thresholds" is checked and add a couple more Motions and observe Thresholds
7. Remove Motion entries until only the first one with a Threshold of 0 is left
8. Add more Motions

Actual results: After removing all Motions except the first Motion with a Threshold of 0 and then adding new Motions new Thresholds are not automatically calculated when "Automate Thresholds" is checked

Expected results: Motion Thresholds are automatically calculated whenever "Automate Thresholds" is checked, no matter the amount of entries in the Blendtree Motion list

Reproducible with versions: 2022.3.62f1, 6000.0.50f1, 6000.1.4f1, 6000.2.0b2

Tested on (OS): Windows 11