Fix swipe-down crash

[vdhamer]

Swiping down currently does 2 things:

1. Deletes the content of the database
2. Reloads the content of the database

When adding #1, the crash started showing up. It is CoreData complaining about mixing threads aka contexts.
Probably not a data race issue, because Swift 6 doesn’t have any warnings.
Seems to happen if swiping down takes place during either reloading or before prev deletion finishes.

Questions:
? Does crash go away when compiling for Swift 6 (unlikely, but maybe error message is more specific) ?
? Does it happen when deletion and reloading occur simultaneously ?
? Under what thread is deletion done anyway ? Reloading is done on multiple background threads.
? Any pattern visible in when it happens ? Doesn’t seen to crash if everything has completed before swipe.