Fixes inventory bugs
Created by: clusterfack
Fixes #4605 (closed) Fixes #4628 (closed)
I found out why these were being improperly pooled, thanks to skowron for producing a case to reproduce and view the variables of. On login or when reset_screen() was called for a mob that had an inventory open the inventory obj/screen's were being pooled and being reused elsewhere on other objects.
Hilarity ensues!
Updates the spellmaster fix to bring it in line with the new system to prevent improperly pooled screen objects.