Merge pull request #353 from cameronwhite/fix-conetwist-nans

Fix a potential division by zero for cone twist constraints.

src/BulletDynamics/ConstraintSolver/btConeTwistConstraint.cpp

@@ -779,6 +779,8 @@ void btConeTwistConstraint::calcAngleInfo2(const btTransform& transA, const btTr
 				target.normalize();
 				m_swingAxis = -ivB.cross(target);
                                 m_swingCorrection = m_swingAxis.length();
+
+                                if (!btFuzzyZero(m_swingCorrection))
                                     m_swingAxis.normalize();
 			}
 		}