fix : prevent breakdown when citizen_density (Initial Agent Density s…

[colinfrisch]

🐛 Bug fix

Noticed tiny bug on civil violence : the model breaks down when citizen_density (Initial Agent Density slider) is set to 0.
Fix is : model density starts now at 0.1

[github-actions]

Performance benchmarks:

Model	Size	Init time [95% CI]	Run time [95% CI]
BoltzmannWealth	small	🔵 +2.4% [+1.6%, +3.2%]	🔵 +0.4% [+0.2%, +0.5%]
BoltzmannWealth	large	🔵 -0.3% [-0.7%, -0.0%]	🔵 -0.4% [-0.8%, -0.0%]
Schelling	small	🔵 -0.0% [-0.2%, +0.1%]	🔵 -0.2% [-0.4%, -0.0%]
Schelling	large	🔵 +0.7% [-0.8%, +3.0%]	🔵 +0.2% [-0.3%, +0.7%]
WolfSheep	small	🔵 -0.3% [-0.5%, -0.1%]	🔵 +0.2% [-0.1%, +0.4%]
WolfSheep	large	🔵 -0.6% [-1.2%, -0.3%]	🔵 +0.9% [+0.3%, +1.6%]
BoidFlockers	small	🔵 +1.6% [+0.8%, +2.4%]	🔵 +0.3% [-0.1%, +0.6%]
BoidFlockers	large	🔵 +1.7% [+1.0%, +2.3%]	🔵 +0.7% [+0.5%, +0.9%]

[EwoutH]

Thanks for spotting and fixing this, I think it makes sense.

I will leave the PR open for ~24 hours for additional comments/reviews.

[tpike3]

LGTM