Core/SAI: do not pass old creatureData to UpdateEntry() and keep current health when changing a NPC's entry.

Port From (https://github.com/TrinityCore/TrinityCore/commit/62f5d9b46bd20faf90dd973e2786d1517b1b3bd2)

Source/Game/AI/SmartScripts/SmartScript.cs

@@ -960,7 +960,7 @@ namespace Game.AI
                 {
                     foreach (var target in targets)
                         if (IsCreature(target))
-                            target.ToCreature().UpdateEntry(e.Action.updateTemplate.creature, target.ToCreature().GetCreatureData(), e.Action.updateTemplate.updateLevel != 0);
+                            target.ToCreature().UpdateEntry(e.Action.updateTemplate.creature, null, e.Action.updateTemplate.updateLevel != 0);
                     break;
                 }
                 case SmartActions.Die:

Source/Game/Entities/Creature/Creature.cs

@@ -370,7 +370,12 @@ namespace Game.Entities
             if (updateLevel)
                 SelectLevel();
             else
+            {
+                ulong previousHealth = GetHealth();
                 UpdateLevelDependantStats(); // We still re-initialize level dependant stats on entry update
+                if (previousHealth > 0)
+                    SetHealth(previousHealth);
+            }
 
             SetMeleeDamageSchool((SpellSchools)cInfo.DmgSchool);
             SetStatFlatModifier(UnitMods.ResistanceHoly, UnitModifierFlatType.Base, cInfo.Resistance[(int)SpellSchools.Holy]);