Fixed collision detection in probes

This was a problem before when the probe hit an object that was further than
another object first. Now we traverse all objects all the time to find the
closest one. \o/

projectile.go

@@ -62,7 +62,9 @@ func (p *Projectile) Tick(g *game) {
 			collision, _, pos := v.RectIntersection(obj.Bounds, p.Position, travel)
 			if collision {
 				arrived = true
-				p.Position = pos
+				if pos != nil {
+					p.Position = *pos
+				}
 				obj.Hp -= p.Damage
 				// if obj.Hp < 0 {
 				// 	delete(g.obstacles, i)
@@ -70,7 +72,9 @@ func (p *Projectile) Tick(g *game) {
 			}
 		}
 	} else {
-		p.Position = pos
+		if pos != nil {
+			p.Position = *pos
+		}
 	}
 
 	if arrived || hit_player {