Bugfix. Thanks to Martin Weiser

[[Imported from SVN: r648]]

istl/matrix.hh

@@ -123,6 +123,7 @@ namespace Dune {
     {
       for (unsigned int i=0; i<data_.size(); i++)
         data_[i] = t;
+      return *this;
     }
 
     /** \brief The index operator */