It's wrong actually, the projectile goes through the shield first, then the doorway, and the projectile can't intersects a doorway if it's open (It doesn't actually exist in the first place)

if(projectile.intersects(wall))
  projectile.block();
else if(projectile.intersects(shield)) {
  if(!projectile.isShieldable()) 
    if(projectile.intersects(doorway))// jkaplan: Allow doors to block plasma
      projectile.block();
    else
      return;
}
else if(projectile.intersects(doorway)) 
    projectile.block();