Error when solving a simulation with parameter values with inputs that affect the timescale

[TomTranter]

Describe the bug
Line 408 in simulation evaluates the model timescale without passing inputs and cannot find the electrode height in the example below. Quick fix to use the evaluated timescale on the solution object

To Reproduce

model = pybamm.lithium_ion.SPM()
# load parameter values and process model and geometry
param = model.default_parameter_values
param.update({"Electrode height [m]": "[input]"})
# solve model for 1 minute
t_eval = np.linspace(0, 60, 11)
inputs = {"Electrode height [m]": 0.2}
sim = pybamm.Simulation(model=model, parameter_values=param)
sim.solve(t_eval=t_eval, inputs=inputs)

Expected behaviour
model runs with no issues