sched_timing_today() needs a default rollover hour

When unset it was reverting to the V1 code.

https://forums.ankiweb.net/t/daily-counts-are-reset-on-sync/3441/16

rslib/src/sched/mod.rs

@@ -37,7 +37,7 @@ impl Collection {
 
         let rollover_hour = match self.sched_ver() {
             SchedulerVersion::V1 => None,
-            SchedulerVersion::V2 => self.get_v2_rollover(),
+            SchedulerVersion::V2 => self.get_v2_rollover().or(Some(4)),
         };
 
         Ok(sched_timing_today(