Add default MELEE ammo to all weapons that use it.

The game adds melee ammo to the player every time they respawn or change class. However, if players have their ammo stripped by any mechanism and the weapons returned to them, the melee ammo isn't given. An example of this can be seen on fun_de_arena, where a player_weaponstrip entity removes all the players' weapons, and then a game_player_equip entity gives them some new ones. When the new weapons are given, the players are not given any melee ammo, breaking every weapon's second attack.

This change solves that issue by specifying a default amount of melee ammo for all weapons that use it, ensuring that player weapons will always function correctly.