How to reproduce:
1. Create a new project in your preferred workspace and open it
2. Connect it to Perforce
3. In P4V create a new empty changeset
4. Back in Unity open the VCS Window and refresh it
4. Observe the window's top button bar (The "Delete Empty Changesets" button next to the "Editor Settings" button is missing)
5. Expand the newly created empty changeset (The button should now appear)

Expected result: the "Delete Empty Changesets" button is always shown while there are empty changesets in the workspace
Actual result: the "Delete Empty Changesets" button is missing even when there are empty changesets in the workspace.

Reproducible in: 2019.3.0a12, 2019.2.1f1, 2019.1.14f1, 2018.4.6f1, 2017.4.31f1

Note: this reproduces both when the empty changeset is created outside of the Editor (P4V) and when It's created through code (Example: using Provider.Checkout to a new changeset) If there are multiple empty changesets and only one of them has been expanded then only the expanded one will get deleted when the "Delete Empty Changesets" button is clicked.