Fill y0 with zeroes if not of the correct shape

[schneiderfelipe]

It is a common use case, most of the concentrations in a complex reaction network will be zero. So assume them zero if some are missing.

overreact/overreact/simulate.py

Lines 58 to 60 in ae55264

	def get_y(
	dydt, y0, t_span=None, method="Radau", rtol=1e-3, atol=1e-6, max_time=1 * 60 * 60
	):