Fix bug in DenseSparseMatrix::ToDenseMatrix().

Change-Id: I74a1a03149d74fbc4268ec3ce9d20e09746a7227

internal/ceres/dense_sparse_matrix.cc

diff --git a/internal/ceres/dense_sparse_matrix.cc b/internal/ceres/dense_sparse_matrix.cc
index 7fb7b83..e18a507 100644
--- a/internal/ceres/dense_sparse_matrix.cc
+++ b/internal/ceres/dense_sparse_matrix.cc
@@ -117,7 +117,7 @@
 }
 
 void DenseSparseMatrix::ToDenseMatrix(Matrix* dense_matrix) const {
-  *dense_matrix = m_;
+  *dense_matrix = m_.block(0, 0, num_rows(), num_cols());
 }
 
 #ifndef CERES_NO_PROTOCOL_BUFFERS