Pocketmine-mp: Effects can be given to non-Living classes

[thebigsmileXD]

Issue description

Effects can be given to non-Living.php classes like: Items, Arrows, FallingSand and cause the Level to freeze
Only Living classes are actually _tickable_ by effects in vanilla (Mobs + Human)

Steps to reproduce the issue

1. Apply an effect to a mentioned type above
2. Could not tick level, getAmplifier/Effect/id on null (varies)

OS and versions

• PocketMine-MP: https://jenkins.pmmp.io/view/All/job/PocketMine-MP/69/artifact/PocketMine-MP_1.6.2dev-69_966e4bf8_API-3.0.0-ALPHA5.phar
• PHP: 7.0.1

Crashdump, backtrace or other files

• Later, really busy at work right now

[dktapps]

tl;dr: entities are a confusing inconsistent mess. Same thing applies with attributes.

[thebigsmileXD]

https://giphy.com/gifs/perfect-read-didnt-gGh4I6osbjyRa

[jasonwynn10]

Shouldn't special arrows be able to have effects? or is it just the particles that follow them?

[dktapps]

@jasonwynn10 no, tipped arrows have metadata for potion particles.

[Muqsit]

I don't know if this would be a valid fix but eh..

class Projectile extends Entity {
    public function addEffect(Effect $effect){
        throw new \Error("really...");
    }
}

Or maybe just move the function from Entity to Living and everything will be alright.

[mal0ne-23]

Or maybe just move the function from Entity to Living and everything will be alright.

I think this is a valid fix, why check if the entity is living, just put it in the Living class and no extra checks need to be done.