Fix typo in CBaseCombatWeapon::WeaponClassFromString

[meatspace]

credit goes to Petercov for finding this not me

(i have no idea what this fixes/breaks)

Does this PR close any issues?

not that I know of

PR Checklist

• [*] My PR follows all guidelines in the CONTRIBUTING.md file
• [*] My PR targets a develop branch OR targets another branch with a specific goal in mind

[Blixibon]

I wrote this code several years ago to try to group weapons together in Mapbase's dynamic interaction expansions. This typo wouldn't have presented there, but I don't think there would be anything negatively affected by fixing this.