ISTLSolverEbos: throw NumericalIssue instead of LinearSolverProblem

the former is caught by `ebos`, while the latter isn't. Alternatively,
this can be fixed by deriving `LinearSolverProblem` from
`NumericalIssue`, if preferred.

opm/autodiff/ParallelOverlappingILU0.hpp

@@ -935,7 +935,7 @@ protected:
                 milun_decomposition( A, iluIteration, milu, *ILU, *reorderer, *inverseReorderer );
             }
         }
-        catch ( const Dune::MatrixBlockError& error )
+        catch (const Dune::MatrixBlockError& error)
         {
             message = error.what();
             std::cerr<<"Exception occured on process " << rank << " during " <<