cleanup(reader/handler): calling store.UpdateFeed and store.UpdateFeedError in a defer function

[shizunge]

This makes sure that we are always calling the following functions:

• originalFeed.ScheduleNextCheck
• store.UpdateFeed
• store.UpdateFeedError And we only call them in a single place regardless which branch is taken inside function.

The store functions within them will udpate the value in database.

This change aims to reduce "unknown unknowns" in the codes. With this change, we won't miss calling above functions.

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• [ ] I have tested my changes
• [ ] There is no breaking changes
• [ ] I really tested my changes and there is no regression
• [ ] Ideally, my commit messages follow the Conventional Commits specification
• [ ] I read this document: https://miniflux.app/faq.html#pull-request