Bugfix: If some degree of freedom is truncated, then don't do anything for that component

dune/solvers/iterationsteps/trustregiongsstep.cc

@@ -74,6 +74,11 @@ void TrustRegionGSStep<MatrixType, VectorType>::iterate()
                 }
 
             } else  {
+
+                // If the corresponding dof was truncated, then compute no correction
+                if (diag==0 && r == 0)
+                    continue;
+
                 // 1d problem is concave or linear.
                 // Minimum is attained at one of the boundaries
                 field_type lBound = obstacles[i].lower(j);