Fixed hands model error

[ERROR] lua/includes/modules/player_manager.lua:63: bad argument #1 to
'lower' (string expected, got nil)
1. lower - [C]:-1
2. TranslateToPlayerModelName -
lua/includes/modules/player_manager.lua:63
3. RunClass -
gamemodes/darkrp/gamemode/modules/base/sh_playerclass.lua:11
4. Call - gamemodes/base/gamemode/player.lua:290
5. DoSetup - gamemodes/base/entities/entities/gmod_hands.lua:25
6. SetupHands - lua/includes/extensions/player.lua:202
7. PlayerSpawn - gamemodes/base/gamemode/player.lua:261
8. unknown -
gamemodes/darkrp/gamemode/modules/base/sv_gamemode_functions.lua:660