Handle errors when tickers can't be loaded

[stkerr]

Description

This PR gracefully handles errors when certain tickers can't be loaded as part of /stocks/ca commands. This can happen for certain tickers like SPY. When a ticker can't be loaded, it is removed from the comparison set and the command continues if possible. An example of what happens is in the screenshot below.

How has this been tested?

Manual testing and pytest

Checklist:

• Update our Hugo documentation following these guidelines.
• Update our tests following these guidelines.
• Make sure you are following our CONTRIBUTING guidelines.
• If a feature was added make sure to add it to the corresponding scripts file.

Others

• I have performed a self-review of my own code.
• I have commented my code, particularly in hard-to-understand areas.
• My code passes all the checks pylint, flake8, black, ... To speed up development you should run pre-commit install.
• New and existing unit tests pass locally with my changes. You can test this locally using pytest tests/....

[DidierRLopes]

This is a nice addition.

Is this ready to be reviewed?

[stkerr]

@DidierRLopes all cleaned up and ready for your review!

[DidierRLopes]

Thank you for this, this is a very nice one.

I believe someone had in fact ask for this before at some point!