[TF2] Fix MvM upgrade panel persisting across map changes

[SanyaKor]

Fix MvM upgrade panel persisting after a server change

In MvM, the upgrade panel can be opened by pressing the inspect key (F by default) to view upgrades or by touching an upgrade station zone to buy them. If the player changes servers without closing the panel, it can remain visible with state from the previous server.

Note

This does not transfer purchased upgrades between servers. Only the upgrade panel remains visible; the upgrades themselves are still server-side.

Video

YouTube demonstration

Cause and fix

This happened because CHudUpgradePanel did not override LevelShutdown(). It therefore used the default CHudElement handler, which returns without cleaning up any panel state:

virtual void LevelShutdown( void ) { ... };

This change overrides the method to clear and hide the panel during level shutdown. It calls CHudElement::SetActive(false) directly to avoid sending MvM_UpgradesDone while leaving the server.