plot_final_wealth_hist() sometimes breaks

[divilian]

The plot_final_wealth_hist() function sometimes breaks, because when it's "final"-ly plotted, most or all agents are dead. So it has (say) only zero or one wealth to plot a histogram for.

You can reproduce with:

SPECnet simulation parameters:
   animation_delay = 20
   init_sg_lvl = 50
   k = 2
   make_anims = false
   make_sim_plots = true
   max_iters = 250
   metabolic_rate = 5
   N = 50
   num_boot_samples = 1000
   openness = 0.0
   proto_threshold = 65
   random_seed = 12369
   salary = 10
   SF_degree = 2
   SF_edges = 40
   starvation_period = 80
   whichGraph = erdos_renyi
   white_noise_intensity = 25.0
   β = 0.2
   λ = 1

Consider: in the state of the project as of today, when is the appropriate place to generate this histogram?