fix #234. Also another possible bug.

[semaphoreP]

Addresses issue #234 (see plots below). Also I noticed that line 319 should be if np.std(self.post[:, index_num]) > 0: because i indexes into the param_list array, not self.post.

Reproducing the issue #234, now behavior is good:

corner_figure_median_95 = result_copy.plot_corner(
    param_list = ['sma1', 'ecc1', 'inc1', 'aop1', 'pan1', 'tau1'],
    show_titles = True
)

corner_figure_median_95 = result_copy.plot_corner(
    param_list = ['tau1','sma1','pan1','aop1','ecc1','inc1'],
    show_titles = True
)

[sblunt]

Looks good to me. Once @adj-smith confirms it fixes issue #234, it I'll pull it in.

[adj-smith]

Yes, this works for me now as well!

[sblunt]

Excellent! Thanks @semaphoreP!