optional jacobian fix

gtsam/base/OptionalJacobian.h

@@ -94,9 +94,11 @@ public:
   /// Constructor that will resize a dynamic matrix (unless already correct)
   OptionalJacobian(Eigen::MatrixXd* dynamic) :
       map_(nullptr) {
+	if (dynamic) {
       dynamic->resize(Rows, Cols); // no malloc if correct size
       usurp(dynamic->data());
 	}
+  }
 
   /**
    * @brief Constructor from an Eigen::Ref *value*. Will not usurp if dimension is wrong