Define Overwatch Gasmask as empty class

The Gasmask classname will be saved in Player Profil, if a player
connect with this classname will the error (No entry) displayed to each
player....
This 'fix' the damn Overwatch CopyPast Gasmask Mod
Merge pull request #550 from Skaronator/master

Define Overwatch Gasmask as empty class, thanks