Do the command validity checks all at once

[HarHarLinks]

Observed Behavior

parsing time sometimes fails, so i retry to find what works.
only then the bot complains that the reminder already exists.

Expected Behavior

Complain about all parsing issues at once so I can fix all in one go

Steps to Reproduce

• !r cron 0 12 28 * *; test
• !r next monday noon; test
• !r july 1 noon; test

Environment

• Bot version: latest
• Deployment method: docker
• Operating system: debian
• Server timezone: Europe/Berlin

Proposed Fix (optional)

If a parsing step fails, continue parsing to try find all issues