I released an updated and improved version of the game, most  bugs have been fixed and the healthpack-system has also been improved.

Changes;

-Zombies deal more damage now.

-The game does not crash anymore.

-Audio for empty guns has been fixed.

-Audio for reloading has been added.

-You can now stack healthpacks and use them via rightclick.

-zombies are smaller and more slippery to avoid getting stuck.

-trees are slightly transparent now so you can spot enemies hiding beneath.

-All invisible walls are now where they actually belong.

-Bullets now  have right rotation.

The next update will bring along an "endless" mode, it will take a decent while tho.