Remove explicit assert in Blockstore::get_slot_entries_in_block() (an…

…za-xyz#1258)

This is a private function and the callers should NOT be calling with an
empty completed range vector. Regardless, it is safer to just return an
empty Entry vector should an empty CompletedRanges be provided as input.

ledger/src/blockstore.rs

@@ -3515,10 +3515,12 @@ impl Blockstore {
         completed_ranges: CompletedRanges,
         slot_meta: Option<&SlotMeta>,
     ) -> Result<Vec<Entry>> {
-        assert!(!completed_ranges.is_empty());
-
-        let (all_ranges_start_index, _) = *completed_ranges.first().unwrap();
-        let (_, all_ranges_end_index) = *completed_ranges.last().unwrap();
+        let Some((all_ranges_start_index, _)) = completed_ranges.first().copied() else {
+            return Ok(vec![]);
+        };
+        let Some((_, all_ranges_end_index)) = completed_ranges.last().copied() else {
+            return Ok(vec![]);
+        };
         let keys =
             (all_ranges_start_index..=all_ranges_end_index).map(|index| (slot, u64::from(index)));