Fixed uninitialized variables in unit tests.

Fixed /W4 warning C4512 (LU was left out on purpose).

Eigen/src/Sparse/AmbiVector.h

@@ -370,6 +370,9 @@ class AmbiVector<_Scalar>::Iterator
     int m_cachedIndex;          // current coordinate
     Scalar m_cachedValue;       // current value
     bool m_isDense;             // mode of the vector
+
+  private:
+    Iterator& operator=(const Iterator&);
 };