PlotForecastPDF: Background problem in Nord3

Hi @erifarov (and @aho),

As explained here es/sunset#82 (closed) I have commented the line https://earth.bsc.es/gitlab/external/cstools/-/blob/master/R/PlotForecastPDF.R#L426 and I got a better result.

I haven't tested in WS or compared differences yet. In any case, I am not sure if this is the way to go or there is a better approach to solve this problem.

Please, let me know any opinion you have on this.

Cheers,

Núria