[bugfix] Properly unset all entries in the recompute_ BitSetVector

This fixes the previous patch.

dune/solvers/iterationsteps/mmgstep.cc

@@ -34,7 +34,8 @@ preprocess()
     recompute_.resize(this->mgTransfer_.size());
     for (size_t i=0; i<this->mgTransfer_.size(); i++)
     {
-        recompute_[i].resize(hasObstacleHierarchy_[i]->size(), false);
+        recompute_[i].resize(hasObstacleHierarchy_[i]->size());
+        recompute_[i].unsetAll();
         dynamic_cast<TruncatedMGTransfer<VectorType>*>(this->mgTransfer_[i])->setRecomputeBitField(&recompute_[i]);
     }