Fix crash when switching back to last item when item was removed

[SamVanheer]

This is the fix for #1815 that was added in a previous update to the game. This PR applies the fix to the SDK.

[malortie]

This change would also need to be applied to Deathmatch Classic and Ricochet code in the SDK.

https://github.com/ValveSoftware/halflife/blob/c7240b965743a53a29491dd49320c88eecf6257b/dmc/dlls/player.cpp#L3709-L3710

https://github.com/ValveSoftware/halflife/blob/c7240b965743a53a29491dd49320c88eecf6257b/ricochet/dlls/player.cpp#L3806-L3807