[BUG]: Simulate charts are broken when the simulation result is empty or in bad state.

[liunelson]

Describe the bug

Holly and I encountered this issue with `Simulate``.

When we ran this model & its configuration, the line charts are broken.

This seems to occur when the configuration is problematic (initial expressions are set to integers instead of floats) and causes Simulate to return some unexpected result (empty dataframe?).

To Reproduce
Steps to reproduce the behavior:

1. Go to this workflow https://app.staging.terarium.ai/projects/eb16a7a8-17f1-4295-a938-146969f8f1a1/workflow/b9be7f12-0b70-469c-a66f-3030f8e3aa2d
2. Go to this Simulate operator https://app.staging.terarium.ai/projects/eb16a7a8-17f1-4295-a938-146969f8f1a1/workflow/b9be7f12-0b70-469c-a66f-3030f8e3aa2d?operator=2ba8e5d4-f191-4771-a1ba-3c6a170e061d
3. Run this with the Euler solver option
4. See broken line chart

Expected behavior
It's unclear what pyciemss-service.simulate returned but the chart should not break like this.

[YohannParis]

@liunelson isn't this issue related to that integer/float bug with PyCIEMSS?
ciemss/pyciemss#618

[liunelson]

@YohannParis This can be reproduced that way (by using integers as initial condition expressions). However, no error was raised.