mingen is erased when generating TS for hydro

[flomnes]

Branch develop, commit b842503.

See src/libs/antares/study/parts/hydro/series.cpp:160

void DataSeriesHydro::resizeGenerationTS(uint nbSeries)
{
    storage.reset(nbSeries, DAYS_PER_YEAR);
    ror.reset(nbSeries, HOURS_PER_YEAR);
    mingen.reset(nbSeries, HOURS_PER_YEAR);

    generationTScount_ = nbSeries;
}

Also src/solver/ts-generator/generator.cpp:49

// Hydro
if (params.timeSeriesToGenerate & Data::timeSeriesHydro)
{
    Data::DataSeriesHydro* const series = area.hydro.series;
    const uint nbSeries = params.nbTimeSeriesHydro;
    series->resizeGenerationTS(nbSeries);
}

I was able to reproduce on study valid-named-mps/binding-constraints, by setting mingen to 1 for area AT. The upper bound is as expected (problem-1-1--optim-nb-1.mps)

 UP BNDVALUE  HydProd::area<at>::hour<0>  4176.178291061

but the lower bound is absent, meaning it is =0 (expected 1).