set broadphase handle to zero when destructing a btCollisionWorld, just in case a collision object/ rigid body is re-used.

Thanks to Ole for reporting

Fix a bug , causing some deep penetrations to be missed. Not likely to have impacted many users, as such deep penetrations should have prevented in the first place.
Thanks a lot to Andy O'Neil for reporting and reproduction case.

src/BulletCollision/NarrowPhaseCollision/btGjkPairDetector.cpp

@@ -150,7 +150,8 @@ void btGjkPairDetector::getClosestPoints(const ClosestPointInput& input,Result&
 			// potential exit, they don't overlap
 			if ((delta > btScalar(0.0)) && (delta * delta > squaredDistance * input.m_maximumDistanceSquared)) 
 			{
-				checkPenetration = false;
+				checkSimplex=true;
+				//checkPenetration = false;
 				break;
 			}