[SIMD] fix Solvers - if one lane has zero initial residual

If one lane has zero residual (e.g. the RHS and initial guess is zero) the division in the factor for the minimizing and orthogonalization is handled explicitly to avoid NaNs.

dune/istl/solver.hh

@@ -470,13 +470,13 @@ namespace Dune
         }
         _def = def;
         _i = i;
-        _res.converged = (Simd::allTrue(def<_def0*_parent._reduction) || Simd::max(def)<1E-30);    // convergence check
+        _res.converged = (Simd::allTrue(def<_def0*_parent._reduction || def<real_type(1E-30)));    // convergence check
         return _res.converged;
       }
 
     protected:
       void finalize(){
-        _res.converged = (Simd::allTrue(_def<_def0*_parent._reduction) || Simd::max(_def)<1E-30);
+        _res.converged = (Simd::allTrue(_def<_def0*_parent._reduction || _def<real_type(1E-30)));
         _res.iterations = _i;
         _res.reduction = static_cast<double>(Simd::max(_def/_def0));
         _res.conv_rate  = pow(_res.reduction,1.0/_i);