Minor fix for CBasePlayerWeapon::ExtractAmmo

This get rid of the warning with "iReturn not being initialized" with debug binaries for weapons which doesn't use ammo (crowbar for example).
Same fix applied to Ricochet
Same fix applied to Deathmatch Classic
Merge pull request #1582 from JoelTroch/master

Minor fix for CBasePlayerWeapon::ExtractAmmo