[Fix] Boats should never get FixZ'd (#2246)

* Boats should never get FixZ'd

* Use member variable to avoid repetitive checks

* Resolve comments from review

* Fix return type

zone/mob.h

@@ -630,7 +630,9 @@ public:
 	inline const float GetSize() const { return size; }
 	inline const float GetBaseSize() const { return base_size; }
 	inline const GravityBehavior GetFlyMode() const { return flymode; }
-	bool IsBoat() const;
+	bool IsBoat() const; // Checks races - used on mob instantiation
+	bool GetIsBoat() const { return is_boat; } // Set on instantiation for speed
+	void SetIsBoat(bool boat) { is_boat = boat; }
 	bool IsControllableBoat() const;
 	inline const bool AlwaysAggro() const { return always_aggro; }
 
@@ -1664,6 +1666,7 @@ protected:
 	bool endur_upkeep;
 	bool degenerating_effects; // true if we have a buff that needs to be recalced every tick
 	bool spawned_in_water;
+	bool is_boat;
 
 	CombatRecord combat_record{};