Fix lower bound when fetching a range of IMAP messages for the sync

[ChristophWurst]

Fixes #2909

When we fetch messages for the initial sync, we use a UID range. There is a bit of logic involved to only fetch roughly $maxResults messages, and we might have a known offset $highestKnownUid to take into account for resumed sync's. The code previously always set the lower range bound to $highestKnownUid + 1, so for the very first sync attempt the range was like 0:$maxResults. If the UIDs of a mailbox start after $maxResults, no messages were returned. And the logic entered an infinite retry loop.

Now, the new logic starts at $min, the lowest known UID reported by the server or at $highestKnownUid, whichever is higher. The upper bound is calculated based on the lower bound.

If my train of thought is not derailing, this should give the correct range to fetch. I can still correctly sync all messages with my test accounts.

TODO

• Fix the bug
• Add tests to verify the fix
• Remove debug logs once we have the confirmation this works from Cannot load mail anymore since upgrade to 1.3.0 #2909 (comment) leaving them in case we have to debug this another time

[ChristophWurst]

@skjnldsv remember

🙊

[skjnldsv]

Code make sense! Did not saw anything crazy! 🚀