sol.graphs() unavailable for collocation problems when min/max bounds are involved

[Kev1CO]

Modify file plot.py

TODO: introduce repeat for the COLLOCATIONS min/max_bounds only for states graphs.
For now the plots in COLLOCATIONS with LINEAR are not giving the right values
nlp.plot[variable].bounds.check_and_adjust_dimensions(n_elements=len(mapping_to_first_index), n_shooting=ns)