Merge branch 'issue/unused-variable' into 'master'

Fix unused variable warning

See merge request amdis/amdis!80

amdis/linearalgebra/mtl/KrylovRunner.hpp

@@ -75,7 +75,7 @@ namespace AMDiS
       iter.set_quite(Environment::infoLevel() == 0);
       iter.suppress_resume(Environment::infoLevel() == 0);
 
-      int error = itlSolver_(*A_, x, b, *P_, iter);
+      [[maybe_unused]] int error = itlSolver_(*A_, x, b, *P_, iter);
 
       stat.iterations = iter.iterations();
       stat.converged = iter.is_converged();