Frequent asserts in multi-thread dispatching after 2.82

[frownmonkey]

I am seeing very frequent asserts (4 per pair per tick) when using a multi-threaded dispatcher that is related to a recent change from 2.81 to 2.82. The code that is directly causing the asserts was added in r2637. This does not happen in a single-threaded model.

The full path to the asserts starts in SpuCatheringCollisionTask.cpp around line 727 in ProcessSpuConvexConvexCollision() where two btConvexPointCloudShape are created on the stack. New btConvexPointCloudShape objects have m_isLocalAabbValid set to false by default. And the setPoints() function is invoked such that AABB recalculation is disabled. When these stack objects are eventually passed on to btGjkPairDetector::getClosestPoints() they have not had recalcLocalAabb() called and m_isLocalAabbValid is still false. This is causing the asserts to arise in the new code from r2637 which invokes getAabb() (line 454/457) on those collision objects.

I can work around this for now by setting m_fixContactNormalDirection in btGjkPairDetector to false. But I'd rather not since the description on the fix sounds rather important.

BTW, thanks for the great work on Bullet.