1.4 Bug fix and balance change

Balance change:

• Reduce minimum damage output at maximum range of the explosion for explosive zombie from 17 to 3.
• Reduce the max health increase of enemies from round change.

Bug fix:

• Fix an issue preventing the fire animation for the pistol from playing.
• Fix a sound concurency issue with all player melee attack.
• Added invisible wall to prevent player from going out enemy range.
• Fix a bug where players could enter an enemy spawn.
• Fix a bug where player could buy the melee weapon when already equiped.
• Fix a bug where ammo crate dropped from ennemies could be picked up with a melee weapon in hand.
• Fix a bug where the Alien would spawn but not move (he was a bit shy).
• Fix a navigation issue with turret zombies that prevented them from moving.
• Fix navigation issue with jumping zombie preventing them from falling.