Recover prev. iteration count and curves for undistributed wells

Rounding errors for `B.mmv(x,y)` are slightly different from
```
Y temp(y);
B-mv(x, temp);
y -= temp;
```

opm/simulators/wells/WellInterface_impl.hpp

@@ -52,6 +52,7 @@ namespace Opm
       , first_perf_(first_perf_index)
       , perf_data_(&perf_data)
     {
+        assert(well.name()==pw_info.name());
         assert(std::is_sorted(perf_data.begin(), perf_data.end(),
                               [](const auto& perf1, const auto& perf2){
                                   return perf1.ecl_index < perf2.ecl_index;