set solution vector to zeros before solve

src/amdis/ProblemStat.inc.hpp

@@ -288,6 +288,7 @@ buildAfterAdapt(AdaptInfo& /*adaptInfo*/, Flag /*flag*/, bool asmMatrix, bool as
   // 3. finish matrix insertion and apply dirichlet boundary conditions
   systemMatrix_->finish(asmMatrix);
   rhs_->finish(asmVector);
+  (*solution_) = 0;
 
   forEachNode_(localView.tree(), [&,this](auto const& rowNode, auto) {
     forEachNode_(localView.tree(), [&,this](auto const& colNode, auto) {