Fix SHWindow plotting routines (plot_spectra and plot_windows) when the number of rows is equal to 1
Fix SHWindow plotting routines (plot_spectra and plot_windows) when the number of rows is equal to 1

MarkWieczorek/SHTOOLS,SHTOOLS/SHTOOLS,MMesch/SHTOOLS,MarkWieczorek/SHTOOLS,SHTOOLS/SHTOOLS,ioshchepkov/SHTOOLS