Always create the log_time timeline (#1763)

crates/re_data_store/src/entity_tree.rs

@@ -40,7 +40,6 @@ impl TimeHistogramPerTimeline {
 // ----------------------------------------------------------------------------
 
 /// Number of messages per time per timeline
-#[derive(Default)]
 pub struct TimesPerTimeline(BTreeMap<Timeline, BTreeSet<TimeInt>>);
 
 impl TimesPerTimeline {
@@ -79,6 +78,13 @@ impl TimesPerTimeline {
     }
 }
 
+// Always ensure we have a default "log_time" timeline.
+impl Default for TimesPerTimeline {
+    fn default() -> Self {
+        Self(BTreeMap::from([(Timeline::log_time(), Default::default())]))
+    }
+}
+
 // ----------------------------------------------------------------------------
 
 /// Tree of entity paths, plus components at the leaves.

crates/re_viewer/src/misc/time_control.rs

@@ -501,11 +501,11 @@ impl TimeControl {
 }
 
 fn min(values: &BTreeSet<TimeInt>) -> TimeInt {
-    *values.iter().next().unwrap()
+    *values.iter().next().unwrap_or(&TimeInt::BEGINNING)
 }
 
 fn max(values: &BTreeSet<TimeInt>) -> TimeInt {
-    *values.iter().rev().next().unwrap()
+    *values.iter().rev().next().unwrap_or(&TimeInt::BEGINNING)
 }
 
 fn range(values: &BTreeSet<TimeInt>) -> TimeRange {