Remove particle forces if it gets destroyed

include/bounce/cloth/force.h

@@ -46,6 +46,9 @@ public:
 
 	//
 	b3Force* GetNext();
+
+	//
+	virtual bool HasParticle(const b3Particle* particle) const = 0;
 protected:
 	friend class b3List2<b3Force>;
 	friend class b3Cloth;

include/bounce/cloth/spring_force.h

@@ -67,6 +67,8 @@ public:
 	float32 GetDampingStiffness() const;
 
 	b3Vec3 GetActionForce() const;
+
+	bool HasParticle(const b3Particle* particle) const;
 private:
 	friend class b3Force;
 	friend class b3Cloth;
@@ -127,4 +129,9 @@ inline b3Vec3 b3SpringForce::GetActionForce() const
 	return m_f;
 }
 
+inline bool b3SpringForce::HasParticle(const b3Particle* particle) const
+{
+	return m_p1 == particle || m_p2 == particle;
+}
+
 #endif