Mobs lose their attack target when converted

When a mob gets converted to another mob while it is attacking something, it will lose its target once the conversion is completed.

Steps to reproduce:

1. For example, summon two skeletons.
2. Make them shoot each other, then make sure they don't die (instant damage potions).
3. Trap one of them in powder snow.
4. Once one skeleton has converted into a stray, it will stop attacking the second skeleton, and the other way around.