Fix for mistaken removal of _draw_grid

[quaquel]

As pointed out by @wang-boyu in #2386, there was a small mistake. I collapsed the drawing of continuous space and old style grid spaces. This fixes that mistake.

ps. I'll try to get some basic unit testing in place for the visualization stuff in the coming days.

[github-actions]

Performance benchmarks:

Model	Size	Init time [95% CI]	Run time [95% CI]
BoltzmannWealth	small	🔵 +2.2% [+0.5%, +4.0%]	🔴 +3.9% [+3.8%, +4.1%]
BoltzmannWealth	large	🔵 +2.8% [+2.4%, +3.2%]	🔴 +4.9% [+4.3%, +5.5%]
Schelling	small	🔵 +0.4% [-0.0%, +0.8%]	🔵 +2.3% [+2.0%, +2.6%]
Schelling	large	🔵 +2.8% [+1.8%, +3.7%]	🔵 +4.1% [+2.5%, +5.8%]
WolfSheep	small	🔴 +3.7% [+3.3%, +4.1%]	🔴 +4.9% [+4.6%, +5.3%]
WolfSheep	large	🔵 +0.6% [-0.5%, +1.7%]	🔵 +0.7% [-3.7%, +6.7%]
BoidFlockers	small	🔵 +0.6% [+0.1%, +1.2%]	🔵 +2.4% [+1.8%, +3.0%]
BoidFlockers	large	🔵 +1.7% [+0.9%, +2.6%]	🔵 +1.8% [+1.3%, +2.2%]