Debug info: Sync interval "0 min" when actually -1 (manual)

[sunkup]

The sync interval in the debug info is taken from AccountSettings and formatted like this:

davx5-ose/app/src/main/kotlin/at/bitfire/davdroid/ui/DebugInfoModel.kt

Line 553 in 0adceb6

accountSettings.getSyncInterval(info.authority)?.let {"${it/60} min"},

The value we get from the account settings (it) may sometimes be -1 (SYNC_INTERVAL_MANUALLY) and "${-1/60} min" then evaluates to "0 min". See an example here.

This is because in java and kotlin Integer division rounds towards zero.

We should fix that when generating the debug info.

Originally posted by @sunkup in https://github.com/bitfireAT/davx5/issues/581#issuecomment-2173312911