Steps to reproduce:
1. Create new Unity project
2. Open Search Index Manager
3. Delete "Assets" index from the list pressing "-"
4. When the list becomes empty, press “-“ again
5. Observe the Console window

Actual results: “-“ button is still active when nothing is present in the list, error “ArgumentOutOfRangeException: Index was out of range. Must be non-negative and less than the size of the collection. Parameter name: index” is thrown in the Console window

Expected results: “-“ button should be inactive if list is empty, only “+” button is active, no errors in the Console window

Reproducible with versions: 6000.0.65f1, 6000.2.15f1
Can’t test with versions: 6000.3.3f1 and higher (Different Index Manager window)

Tested on (OS): macOS Tahoe 26.1 (M1)