[Bleeding] Ignore damage done by LivingEntity.damage(). Fixes BUKKIT-5666

This matches behavior previous to new damage event API of not throwing
events for plugin-triggered damage.

src/main/java/org/bukkit/craftbukkit/event/CraftEventFactory.java

@@ -511,6 +511,8 @@ public class CraftEventFactory {
             cause = DamageCause.MAGIC;
         } else if (source == DamageSource.FALL) {
             cause = DamageCause.FALL;
+        } else if (source == DamageSource.GENERIC) {
+            return new EntityDamageEvent(entity.getBukkitEntity(), null, modifiers);
         }
 
         if (cause != null) {