Exception when running plotter standalone with --use_gnuplot

[csatt]

This bug is in code that isn't even used for IV Swinger 2. I hit it when running the following command from the CLI (needed to get full code coverage):

% ./IV_Swinger_plotter.py --use_gnuplot ~/Desktop/IV_Swinger2_old/Regression/IV_Swinger2/191116_13_03_12/iv_swinger2_191116_13_03_12.csv

This does not fail with the Python 2 code, but with Python 3 it gets the following exception:

Traceback (most recent call last):
File "./IV_Swinger_plotter.py", line 707, in
main()
File "./IV_Swinger_plotter.py", line 702, in main
ivp.run()
File "./IV_Swinger_plotter.py", line 693, in run
ivs_extended.plot_graphs(args, csv_proc)
File "./IV_Swinger_plotter.py", line 502, in plot_graphs
self.plot_with_plotter(gp_command_filename,
File "/Users/csatt/GitHub/IV_Swinger/python3/IV_Swinger.py", line 3234, in plot_with_plotter
self.plot_with_gnuplot(sd_gp_command_filename,
File "/Users/csatt/GitHub/IV_Swinger/python3/IV_Swinger.py", line 3250, in plot_with_gnuplot
self.write_gnuplot_file(sd_gp_command_filename,
File "/Users/csatt/GitHub/IV_Swinger/python3/IV_Swinger.py", line 3162, in write_gnuplot_file
self.adjust_margins()
File "/Users/csatt/GitHub/IV_Swinger/python3/IV_Swinger.py", line 4082, in adjust_margins
if self.plot_max_y < 0.5:
TypeError: '<' not supported between instances of 'NoneType' and 'float'

The problem is that the write_gnuplot_file() method in IV_Swinger.py calls the adjust_margins() method before the plot_max_y property is set by the set_y_range() method. This means plot_max_y has a value of None when the comparison with 0.5 is performed. In Python 2, this doesn't cause an exception because None is treated like 0.0 in the comparison. But Python 3 doesn't allow comparing None to a float.

The call to adjust_margins() needs to be moved after the call to set_y_range().